Method and system for secure cable modem initialization

ABSTRACT

A method and system for secure cable modem initialization in a data-over-cable system is provided using a secure protocol server. The method includes sending a unique identifier, such an Internet Protocol (&#34;IP&#34;) address and a selected time-value, such as an approximate message send time-value, in a configuration file from a protocol server such as a Trivial File Protocol server (&#34;TFTP&#34;). A message integrity value is calculated using the unique identifier, the selected time-value and one or more configuration parameters in a pre-determined order with a cryptographic hashing function. The message integrity value is added to the configuration file. A cable modem receives the configuration file from the TFTP server and uses the message integrity value to authenticate the configuration file and determine if the configuration file was sent within a pre-determined period of time (e.g., 5 seconds) from the TFTP server. If not, the configuration is discarded by the cable modem. The unique identifier and selected time-value uniquely identify the configuration file for the cable modem and help prevent a rouge user from intercepting a valid cable modem configuration file and using it at a later time to initialize a rouge cable modem. The method and system provide improved security for initializing cable modems in a data-over-cable system.

FIELD OF INVENTION

The present invention relates to communications in computer networks.More specifically, it relates to a method and system for secure cablemodem initialization in a data-over-cable system.

BACKGROUND OF THE INVENTION

Cable television networks such as those provided by Comcast CableCommunications, Inc., of Philadelphia, Pa., Cox Communications ofAtlanta Ga., Tele-Communications, Inc., of Englewood Colo., Time-WarnerCable, of Marietta Ga., Continental Cablevision, Inc., of Boston Mass.,and others provide cable television services to a large number ofsubscribers over a large geographical area. The cable televisionnetworks typically are interconnected by cables such as coaxial cablesor a Hybrid Fiber/Coaxial ("HFC") cable system which have data rates ofabout 10 Mega-bits-per-second ("Mbps") to 30+ Mbps.

The Internet, a world-wide-network of interconnected computers, providesmulti-media content including audio, video, graphics and text thatrequires a large bandwidth for downloading and viewing. Most InternetService Providers ("ISPs") allow customers to connect to the Internetvia a serial telephone line from a Public Switched Telephone Network("PSTN") at data rates including 14,400 bps, 28,800 bps, 33,600 bps,56,000 bps and others that are much slower than the about 10 Mbps to 30+Mbps available on a coaxial cable or HFC cable system on a cabletelevision network.

With the explosive growth of the Internet, many customers have desiredto use the larger bandwidth of a cable television network to connect tothe Internet and other computer networks. Cable modems, such as thoseprovided by 3Com Corporation of Santa Clara, Calif., U.S. RoboticsCorporation of Skokie, Ill., and others offer customers higher-speedconnectivity to the Internet, an intranet, Local Area Networks ("LANs")and other computer networks via cable television networks. These cablemodems currently support a data connection to the Internet and othercomputer networks via a cable television network with a data rate of upto 30+ Mbps which is a much larger data rate than can be supported by amodem used over a serial telephone line.

However, most cable television networks provide only uni-directionalcable systems, supporting only a "downstream" data path. A downstreamdata path is the flow of data from a cable system "headend" to acustomer. A cable system headend is a central location in the cabletelevision network that is responsible for sending cable signals in thedownstream direction. A return data path via a telephone network, suchas a public switched telephone network provided by AT&T and others,(i.e., a "telephony return") is typically used for an "upstream" datapath. An upstream data path is the flow of data from the customer backto the cable system headend. A cable television system with an upstreamconnection to a telephony network is called a "data-over-cable systemwith telephony return."

An exemplary data-over-cable system with telephony return includescustomer premise equipment (e.g., a customer computer), a cable modem, acable modem termination system, a cable television network, a publicswitched telephone network, a telephony remote access concentrator and adata network (e.g., the Internet). The cable modem termination systemand the telephony remote access concentrator together are called a"telephony return termination system.".

The cable modem termination system receives data packets from the datanetwork and transmits them downstream via the cable television networkto a cable modem attached to the customer premise equipment. Thecustomer premise equipment sends response data packets to the cablemodem, which sends response data packets upstream via public switchedtelephone network to the telephony remote access concentrator, whichsends the response data packets back to the appropriate host on the datanetwork.

When a cable modem used in the data-over-cable system with telephonyreturn is initialized, a connection is made to both the cable modemtermination system via the cable network and to the telephony remoteaccess concentrator via the public switched telephone network. When acable modem is initialized, it will initialize one or more downstreamchannels (i.e., downstream connections) to the cable modem terminationsystem via the cable network or the telephony remote access concentratorvia the public switched telephone network.

As part of the initialization sequence, a cable modem receives aconfiguration file from a protocol server (e.g., a Trivial File TransferProtocol ("TFTP") server) with multiple configuration parameters used toconfigure and initialize the cable modem. The cable modem performs anumber of tests on the configuration file to confirm the integrity ofthe configuration parameters contained in the configuration file. Forexample, the configuration file typically includes one or more MessageIntegrity Check ("MIC") fields. The MIC fields are created on theprotocol server by performing a cryptographic hashing function on theconfiguration parameters (e.g., with Message Digest 5 ("MD5")), andsending the MIC fields with the configuration file. The cable modemverifies the integrity of the configuration file by using the samecryptographic hashing function on the configuration parameters andcomparing the cryptographic hashing values to cryptographic hashingfunction value in the MIC fields.

There are several problems associated with sending a configuration filefrom a protocol server to a cable modem. A configuration file sent froma protocol server to a cable modem with one or more MIC fields is stillvulnerable to malicious attacks. The configuration file can beintercepted and used by rouge cable modems to attack the data-over-cablesystem or obtain free services on the data-over-cable system. The MICfields allow the integrity of the configuration file to be verified bythe cable modem. However, the MIC fields do not include an identifiersuch as a configuration parameter for a cable modem receiving theconfiguration file, nor do the MIC fields identify a time period duringwhich the configuration information can be used by the cable modem.Thus, the MIC fields, as they are presently used in the configurationfile, do not prevent a malicious user from intercepting and re-using theconfiguration file for use by another "rouge" cable modem at anothertime.

For example, a rouge user could intercept a configuration file sent to alegitimate cable modem. At a later time, the rouge user uses all of theconfiguration information exactly as it was intercepted. The rouge userinitializes the rouge cable modem using the configuration file andregisters the cable modem with a cable modem termination system. Sincethe configuration information was used exactly as it was intercepted,when the cable modem termination system checks the MIC fields, theconfiguration information is verified as valid and the rouge usermasquerades as a "legitimate" cable modem user thereby receiving freeservices or attacking the data-over-cable system.

It is therefore desirable to improve the security for transferringconfiguration information from protocol servers to the cable modems in adata-over-cable system so the configuration information cannot bere-used by other rouge cable modems at another time.

SUMMARY OF THE INVENTION

In accordance with an illustrative embodiment of the present invention,the problems associated with sending configuration information areovercome. A method and system for secure initialization of a networkdevice in a data-over-cable system is provided. The method includesreceiving a request for a first configuration file on a first protocolserver from a first network device, the first configuration fileincluding multiple configuration parameters. A unique identifier (e.g.,a network address) for the first network device is added to the firstconfiguration file. A selected time-value is added to the firstconfiguration file, wherein the selected time-value indicates anapproximate sending time for the first configuration file. A messageintegrity check value is calculated using the unique identifier, theselected time-value and one or more configuration parameters from thefirst configuration file in a pre-determined order to uniquely identifythe configuration information for the first network device. The messageintegrity check value is calculated using a pre-determined cryptographictechnique. The message integrity check value is added to the firstconfiguration file. The first configuration file is sent from the firstprotocol server to the first network device. The first network deviceuses the message integrity check value including the unique identifierand selected time-value to uniquely identify the configurationinformation and prevent another network device from using theconfiguration file at a later time.

In an illustrative embodiment of the present invention, a cable modemreceives a configuration file from a TFTP server. However, the inventionis not limited to cable modems and TFTP servers, and other networkdevices and protocol servers could also be used in a data-over-cablesystem.

In an illustrative embodiment of the present invention, a cable modemsends a Read ReQuest message ("RRQ") to a TFTP server requesting aconfiguration file. The cable modem receives the name of theconfiguration file from a Dynamic Host Configuration Protocol ("DHCP")server during an initialization sequence. The TFTP server obtains theconfiguration file (e.g., from a DHCP server). The TFTP server adds anIP address for the cable modem to the configuration file. The IP addressis an address obtained by the cable modem from a DHCP server during aninitialization sequence and sent to the TFTP server in a TFTP RRQmessage header. However, the TFTP server may also obtain the IP addressfrom other sources (e.g., from a DHCP message). The TFTP server selectsa time-value and adds it to the configuration file. The selectedtime-value indicates an approximate sending time of the configurationfile. A message integrity check value is calculated using the IPaddress, the selected time-value and one or more configurationparameters in a pre-determined order to uniquely identify theconfiguration file for the cable modem. In one embodiment of the presentinvention, the message integrity check value is calculated using MessageDigest 5 ("MD5"). However, other cryptographic techniques may also beused. The message integrity check value with the IP address and selectedtime-value is added to the configuration file. The configuration file issent from the TFTP server to the cable modem as secure configurationinformation.

The cable modem uses the message integrity check value to verify theintegrity of the configuration file, as well as determine a time periodfor which the configuration file is valid. For example, if the cablemodem verifies the integrity of the configuration file but detects theselected time-value for the configuration file is different by apredetermined amount (e.g., 5 seconds) from an internal time value onthe cable modem, the cable modem discards the configuration file.

The method and system of the present invention provide improved securityfor cable modem initialization. For a rouge user to attack adata-over-cable system, the rouge user must intercept a configurationfile from the TFTP server, modify the selected time-value (or IPaddress), re-calculate message integrity value with a rouge time value.The configuration file must then be re-transmitted within apre-determined time period that is used by a cable modem (e.g., 5seconds) for checking the integrity of configuration files.

The rouge user may also have to determine the cryptographic techniquebeing used to create the message integrity value and guess thepre-determined time period that is used by the cable modem for checkingconfiguration files. Since the pre-determined time period that is usedby the cable modem for checking registration request messages is small,the probability a rouge user can successfully attack the data-over-cablesystem is reduced. Thus, the security of cable modem initialization isimproved.

The foregoing and other features and advantages of an illustrativeembodiment of the present invention will be more readily apparent fromthe following detailed description, which proceeds with references tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a cable modem system withtelephony return;

FIG. 2 is a block diagram illustrating a protocol stack for a cablemodem;

FIG. 3 is a block diagram illustrating a Telephony Channel Descriptormessage structure;

FIG. 4 is a block diagram illustrating a Termination System Informationmessage structure;

FIG. 5 is a flow diagram illustrating a method for addressing hosts in acable modem system;

FIG. 6 is a block diagram illustrating a Dynamic Host ConfigurationProtocol message structure;

FIGS. 7A and 7B are a flow diagram illustrating a method for discoveringhosts in a cable modem system;

FIG. 8 is a block diagram illustrating a data-over-cable system for themethod illustrated in FIGS. 7A and 7B;

FIG. 9 is a block diagram illustrating the message flow of the methodillustrated in FIGS. 7A and 7B;

FIGS. 10A and 10B are a flow diagram illustrating a method for resolvinghost addresses in a data-over-cable system;

FIG. 11 is a flow diagram illustrating a method for resolving discoveredhost addresses; and

FIG. 12 a block diagram illustrating the message flow of the methodillustrated in FIG. 10;

FIGS. 13A and 13B are a flow diagram illustrating a method for obtainingaddresses for customer premise equipment;

FIGS. 14A and 14B are a flow diagram illustrating a method for resolvingaddresses for customer premise equipment;

FIGS. 15A and 15B are a flow diagram illustrating a method foraddressing network host interfaces from customer premise equipment;

FIGS. 16A and 16B are a flow diagram illustrating a method for resolvingnetwork host interfaces from customer premise equipment;

FIG. 17 is a block diagram illustrating a message flow for the methodsin FIGS. 15A, 15B, and 16A and 16B;

FIG. 18 is a block diagram illustrating a data-over-cable system forsecure initialization of a cable modem;

FIG. 19 is a flow diagram illustrating a method for secureinitialization for a network device;

FIG. 20 is a flow diagram illustrating a method for secureinitialization for a cable modem;

FIG. 21 is a flow diagram illustrating a method for calculating amessage integrity value;

FIG. 22 is a flow diagram illustrating a method for checking validity ofa cable modem configuration file.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

Cable modem system with telephony return

FIG. 1 is a block diagram illustrating a data-over-cable system withtelephony return 10, hereinafter data-over-cable system 10. Most cableproviders known in the art predominately provide uni-directional cablesystems, supporting only a "downstream" data path. A downstream datapath is the flow of data from a cable television network "headend" tocustomer premise equipment (e.g., a customer's personal computer). Acable television network headend is a central location that isresponsible for sending cable signals in a downstream direction. Areturn path via a telephony network ("telephony return") is typicallyused for an "upstream" data path in uni-directional cable systems. Anupstream data path is the flow of data from customer premise equipmentback to the cable television network headend.

However, data-over-cable system 10 of the present invention may alsoprovide a bi-directional data path (i.e., both downstream and upstream)without telephony return as is also illustrated in FIG. 1 and thepresent invention is not limited to a data-over-cable system withtelephony return. In a data-over cable system without telephony return,customer premise equipment or cable modem has an upstream connection tothe cable modem termination system via a cable television connection, awireless connection, a satellite connection, or a connection via othertechnologies to send data upstream to the cable modem terminationsystem.

Data-over-cable system 10 includes a Cable Modem Termination System("CMTS") 12 connected to a cable television network 14, hereinaftercable network 14. Cable network 14 includes cable television networkssuch as those provided by Comcast Cable Communications, Inc., ofPhiladelphia, Pa., Cox Communications, or Atlanta, Ga.,Tele-Communications, Inc., of Englewood Colo., Time-Warner Cable, ofMarietta, Ga., Continental Cablevision, Inc., of Boston, Mass., andothers. Cable network 14 is connected to a Cable Modem ("CM") 16 with adownstream cable connection.

CM 16 is connected to Customer Premise Equipment ("CPE") 18 such as apersonal computer system via a Cable Modem-to-CPE Interface ("CMC") 20.CM 16 is connected to a Public Switched Telephone Network ("PSTN") 22with an upstream telephony connection. PSTN 22 includes those publicswitched telephone networks provided by AT&T, Regional Bell OperatingCompanies (e.g., Ameritch, U.S. West, Bell Atlantic, Southern BellCommunications, Bell South, NYNEX, and Pacific Telesis Group), GTE, andothers. The upstream telephony connection is any of a standard telephoneline connection, Integrated Services Digital Network ("ISDN")connection, Asymmetric Digital Subscriber Line ("ADSL") connection, orother telephony connection. PSTN 22 is connected to a Telephony RemoteAccess Concentrator ("TRAC") 24. In a data-over cable system withouttelephony return, CM 16 has an upstream connection to CMTS 12 via acable television connection, a wireless connection, a satelliteconnection, or a connection via other technologies to send data upstreamoutside of the telephony return path. An upstream cable televisionconnection via cable network 14 is illustrated in FIG. 1.

FIG. 1 illustrates a telephony modem integral to CM 16. In anotherembodiment of the present invention, the telephony modem is a separatemodem unit external to CM 16 used specifically for connecting with PSTN22. A separate telephony modem includes a connection to CM 16 forexchanging data. CM 16 includes cable modems provided by the 3ComCorporation of Santa Clara, Calif., U.S. Robotics Corporation of Skokie,Ill., and others. In yet another embodiment of the present invention, CM16 includes functionality to connect only to cable network 14 andreceives downstream signals from cable network 14 and sends upstreamsignals to cable network 14 without telephony return. The presentinvention is not limited to cable modems used with telephony return.

CMTS 12 and TRAC 24 may be at a "headend" of cable system 10, or TRAC 24may be located elsewhere and have routing associations to CMTS 12. CMTS12 and TRAC 24 together are called a "Telephony Return TerminationSystem" ("TRTS") 26. TRTS 26 is illustrated by a dashed box in FIG. 1.CMTS 12 and TRAC 24 make up TRTS 26 whether or not they are located atthe headend of cable network 14, and TRAC 24 may in located in adifferent geographic location from CMTS 12. Content severs, operationsservers, administrative servers and maintenance servers used indata-over-cable system 10 (not shown in FIG. 1) may also be in differentlocations. Access points to data-over-cable system 10 are connected toone or more CMTS's 12 or cable headend access points. Suchconfigurations may be "one-to-one", "one-to-many," or "many-to-many,"and may be interconnected to other Local Area Networks ("LANs") or WideArea Networks ("WANs").

TRAC 24 is connected to a data network 28 (e.g., the Internet or anintranet) by a TRAC-Network System Interface 30 ("TRAC-NSI"). CMTS 12 isconnected to data network 28 by a CMTS-Network System Interface("CMTS-NSI") 32. The present invention is not limited to data-over-cablesystem 10 illustrated in FIG. 1, and more or fewer components,connections and interfaces could also be used.

Cable modem protocol stack

FIG. 2 is a block diagram illustrating a protocol stack 36 for CM 16.FIG. 2 illustrates the downstream and upstream protocols used in CM 16.As is known in the art, the Open System Interconnection ("OSI") model isused to describe computer networks. The OSI model consists of sevenlayers including from lowest-to-highest, a physical, data-link, network,transport, session, application and presentation layer. The physicallayer transmits bits over a communication link. The data link layertransmits error free frames of data. The network layer transmits androutes data packets.

For downstream data transmission, CM 16 is connected to cable network 14in a physical layer 38 via a Radio Frequency ("RF") Interface 40. In anillustrative embodiment of the present invention, RF Interface 40 has anoperation frequency range of 50 Mega-Hertz ("MHz") to 1 Giga-Hertz("GHz") and a channel bandwidth of 6 MHz. However, other operationfrequencies may also be used and the invention is not limited to thesefrequencies. RF interface 40 uses a signal modulation method ofQuadrature Amplitude Modulation ("QAM"). As is known in the art, QAM isused as a means of encoding digital information over radio, wire, orfiber optic transmission links. QAM is a combination of amplitude andphase modulation and is an extension of multiphase phase-shift-keying.QAM can have any number of discrete digital levels typically including4, 16, 64 or 256 levels. In one embodiment of the present invention,QAM-64 is used in RF interface 40. However, other operating frequenciesmodulation methods could also be used. For more information on RFinterface 40 see the Institute of Electrical and Electronic Engineers("IEEE") standard 802.14 for cable modems incorporated herein byreference. IEEE standards can be found on the World Wide Web at theUniversal Resource Locator ("URL") "www.ieee.org." However, other RFinterfaces 40 could also be used and the present invention is notlimited to IEEE 802.14 (e.g., RF interfaces from Multimedia CableNetwork Systems ("MCNS") and others can be used).

Above RF interface 40 in a data-link layer 42 is a Medium Access Control("MAC") layer 44. As is known in the art, MAC layer 44 controls accessto a transmission medium via physical layer 38. For more information onMAC layer protocol 44 see IEEE 802.14 for cable modems. However, otherMAC layer protocols 44 could also be used and the present invention isnot limited to IEEE 802.14 MAC layer protocols (e.g., MCNS MAC layerprotocols and others could also be used).

Above MAC layer 44 is an optional link security protocol stack 46. Linksecurity protocol stack 46 prevents authorized users from making a dataconnection from cable network 14. RF interface 40 and MAC layer 44 canalso be used for an upstream connection if data-over-cable system 10 isused without telephony return.

For upstream data transmission with telephony return, CM 16 is connectedto PSTN 22 in physical layer 38 via modem interface 48. TheInternational Telecommunications Union-Telecommunication StandardizationSector ("ITU-T", formerly known as the CCITT) defines standards forcommunication devices identified by "V.xx" series where "xx" is anidentifying number. ITU-T standards can be found on the World Wide Webat the URL "www.itu.ch."

In one embodiment of the present invention, ITU-T V.34 is used as modeminterface 48. As is known in the art, ITU-T V.34 is commonly used in thedata link layer for modem communications and currently allows data ratesas high as 33,600 bits-per-second ("bps"). For more information see theITU-T V.34 standard. However, other modem interfaces or other telephonyinterfaces could also be used.

Above modem interface 48 in data link layer 42 is Point-to-PointProtocol ("PPP") layer 50, hereinafter PPP 50. As is known in the art,PPP is used to encapsulate network layer datagrams over a serialcommunications link. For more information on PPP see InternetEngineering Task Force ("IETF") Request for Comments ("RFC"), RFC-1661,RFC-1662 and RFC-1663 incorporated herein by reference. Information forIETF RFCs can be found on the World Wide Web at URLs "ds.internic.net"or "www.ietf.org."

Above both the downstream and upstream protocol layers in a networklayer 52 is an Internet Protocol ("IP") layer 54. IP layer 54,hereinafter IP 54, roughly corresponds to OSI layer 3, the networklayer, but is typically not defined as part of the OSI model. As isknown in the art, IP 54 is a routing protocol designed to route trafficwithin a network or between networks. For more information on IP 54 seeRFC-791 incorporated herein by reference.

Internet Control Message Protocol ("ICMP") layer 56 is used for networkmanagement. The main functions of ICMP layer 56, hereinafter ICMP 56,include error reporting, reachability testing (e.g., "pinging")congestion control, route-change notification, performance, subnetaddressing and others. Since IP 54 is an unacknowledged protocol,datagrams may be discarded and ICMP 56 is used for error reporting. Formore information on ICMP see RFC-971 incorporated herein by reference.

Above IP 54 and ICMP 56 is a transport layer 58 with User DatagramProtocol layer 60 ("UDP"). UDP layer 60, hereinafter UDP 60, roughlycorresponds to OSI layer 4, the transport layer, but is typically notdefined as part of the OSI model. As is known in the art, UDP 60provides a connectionless mode of communications with datagrams. Formore information on UDP 60 see RFC-768 incorporated herein by reference.

Above the network layer are a Simple Network Management Protocol("SNMP") layer 62, Trivial File Protocol ("TFTP") layer 64, Dynamic HostConfiguration Protocol ("DHCP") layer 66 and a UDP manager 68. SNMPlayer 62 is used to support network management functions. For moreinformation on SNMP layer 62 see RFC-1157 incorporated herein byreference. TFTP layer 64 is a file transfer protocol used to downloadfiles and configuration information. For more information on TFTP layer64 see RFC-1350 incorporated herein by reference. DHCP layer 66 is aprotocol for passing configuration information to hosts on an IP 54network. For more information on DHCP layer 66 see RFC-1541 incorporatedherein by reference. UDP manager 68 distinguishes and routes packets toan appropriate service (e.g., a virtual tunnel). More or few protocollayers could also be used with data-over-cable system 10.

CM 16 supports transmission and reception of IP 54 datagrams asspecified by RFC-791. CMTS 12 and TRAC 24 may perform filtering of IP 54datagrams. CM 16 is configurable for IP 54 datagram filtering torestrict CM 16 and CPE 18 to the use of only their assigned IP 54addresses. CM 16 is configurable for IP 54 datagram UDP 60 portfiltering (i.e., deep filtering).

CM 16 forwards IP 54 datagrams destined to an IP 54 unicast addressacross cable network 14 or PSTN 22. Some routers have security featuresintended to filter out invalid users who alter or masquerade packets asif sent from a valid user. Since routing policy is under the control ofnetwork operators, such filtering is a vendor specific implementation.For example, dedicated interfaces (i.e., Frame Relay) may exist betweenTRAC 24 and CMTS 12 which preclude filtering, or various forms ofvirtual tunneling and reverse virtual tunneling could be used tovirtually source upstream packets from CM 16. For more information onvirtual tunneling see Level 2 Tunneling Protocol ("L2TP") orPoint-to-Point Tunneling Protocol ("PPTP") in IETF draft documentsincorporated herein by reference by Kory Hamzeh, et. al (IETF draftdocuments are precursors to IETF RFCs and are works in progress).

CM 16 also forwards IP 54 datagrams destined to an IP 54 multicastaddress across cable network 14 or PSTN 22. CM 16 is configurable tokeep IP 54 multicast routing tables and to use group membershipprotocols. CM 16 is also capable of IP 54 tunneling upstream through thetelephony path. A CM 16 that wants to send a multicast packet across avirtual tunnel will prepend another IP 54 header, set the destinationaddress in the new header to be the unicast address of CMTS 12 at theother end of the tunnel, and set the IP 54 protocol field to be four,which means the next protocol is IP 54.

CMTS 12 at the other end of the virtual tunnel receives the packet,strips off the encapsulating IP 54 header, and forwards the packet asappropriate. A broadcast IP 54 capability is dependent upon theconfiguration of the direct linkage, if any, between TRAC 24 and CMTS12. CMTS 12, CM 16, and TRAC 24 are capable of routing IP 54 datagramsdestined to an IP 54 broadcast address which is across cable network 14or PSTN 22 if so configured. CM 16 is configurable for IP 54 broadcastdatagram filtering.

An operating environment for CM 16 of the present invention includes aprocessing system with at least one high speed Central Processing Unit("CPU") and a memory system. In accordance with the practices of personsskilled in the art of computer programming, the present invention isdescribed below with reference to acts and symbolic representations ofoperations that are performed by the processing system, unless indicatedotherwise. Such acts and operations are sometimes referred to as being"computer-executed", or "CPU executed."

It will be appreciated that the acts and symbolically representedoperations include the manipulation of electrical signals by the CPU.The electrical system represent data bits which cause a resultingtransformation or reduction of the electrical signal representation, andthe maintenance of data bits at memory locations in the memory system tothereby reconfigure or otherwise alter the CPU's operation, as well asother processing of signals. The memory locations where data bits aremaintained are physical locations that have particular electrical,magnetic, optical, or organic properties corresponding to the data bits.

The data bits may also be maintained on a computer readable mediumincluding magnetic disks, optical disks, organic disks, and any othervolatile or non-volatile mass storage system readable by the CPU. Thecomputer readable medium includes cooperating or interconnected computerreadable media, which exist exclusively on the processing system or isdistributed among multiple interconnected processing systems that may belocal or remote to the processing system.

Initialization of a cable modem with telephony return

When CM 16 is initially powered on, if telephony return is being used,CM 16 will receive a Telephony Channel Descriptor ("TCD") from CMTS 12that is used to provide dialing and access instructions on downstreamchannels via cable network 14. Information in the TCD is used by CM 16to connect to TRAC 24. The TCD is transmitted as a MAC managementmessage with a management type value of TRI₋₋ TCD at a periodic interval(e.g., every 2 seconds). To provide for flexibility, the TCD messageparameters are encoded in a Type/Length/Value ("TLV") form. However,other encoding techniques could also be used. FIG. 3 is a block diagramillustrating a TCD message structure 70 with MAC 44 management header 72and Service Provider Descriptor(s) ("SPD") 74 encoded in TLV format.SPDs 74 are compound TLV encodings that define telephony physical-layercharacteristics that are used by CM 16 to initiate a telephone call. SPD74 is a TLV-encoded data structure that contains sets of dialing andaccess parameters for CM 16 with telephony return. SPD 74 is containedwithin TCD message 70. There may be multiple SPD 74 encodings within asingle TCD message 70. There is at least one SPD 74 in TCD message 70.SPD 74 parameters are encoded as SPD-TLV tuples. SPD 74 contains theparameters shown in Table 1 and may contain optional vendor specificparameters. However, more or fewer parameters could also be used in SPD74.

                  TABLE 1                                                         ______________________________________                                        SPD 74 Parameter                                                                            Description                                                     ______________________________________                                        Factory Default Flag                                                                        Boolean value, if TRUE(1), indicates a                                        SPD which should be used by CM 16.                              Service Provider Name                                                                       This parameter includes the name of a                                         service provider. Format is standard                                          ASCII string composed of numbers and                                          letters.                                                        Telephone Numbers                                                                           These parameters contain telephone                                            numbers that CM 16 uses to initiate a                                         telephony modem link during a login                                           process. Connections are attempted in                                         ascending numeric order (i.e., Phone                                          Number 1, Phone Number 2 . . . ). The SPD                                     contains a valid telephony dial string as                                     the primary dial string (Phone Number 1),                                     secondary dial-strings are optional.                                          Format is ASCII string(s) composed of:                                        any sequence of numbers, pound "#" and                                        star "*" keys and comma character ","                                         used to indicate a two second pause in                                        dialing.                                                        Connection Threshold                                                                        The number of sequential connection                                           failures before indicating connection                                         failure. A dial attempt that does not result                                  in an answer and connection after no                                          more than ten rings is considered a                                           failure. The default value is one.                              Login User Name                                                                             This contains a user name CM 16 will use                                      an authentication protocol over the                                           telephone link during the initialization                                      procedure. Format is a monolithic                                             sequence of alphanumeric characters in                                        an ASCII string composed of numbers                                           and letters.                                                    Login Password                                                                              This contains a password that CM 16 will                                      use during authentication over a                                              telephone link during the initialization                                      procedure. Format is a monolithic                                             sequence of alphanumeric characters in                                        an ASCII string composed of numbers                                           and letters.                                                    DHCP Authenticate                                                                           Boolean value, reserved to indicate that                                      CM 16 uses a specific indicated DHCP 66                                       Server (see next parameter) for a DHCP                                        66 Client and BOOTP Relay Process                                             when TRUE (one). The default is FALSE                                         (zero) which allows any DHCP 66 Server.                         DHCP Server   IP 54 address value of a DHCP 66 Server                                       CM 16 uses for DHCP 66 Client and                                             BOOTP Relay Process. If this attribute is                                     present and DHCP 66 Authenticate                                              attribute is TRUE(1). The default value is                                    integer zero.                                                   RADIUS Realm  The realm name is a string that defines a                                     RADIUS server domain. Format is a                                             monolithic sequence of alphanumeric                                           characters in an ACSII string composed                                        of numbers and letters.                                         PPP Authentication                                                                          This parameter instructs the telephone                                        modem which authentication procedure to                                       perform over the telephone link.                                Demand Dial Timer                                                                           This parameter indicates time (in                                             seconds) of inactive networking time that                                     will be allowed to elapse before hanging                                      up a telephone connection at CM 16. If                                        this optional parameter is not present, or                                    set to zero, then the demand dial feature                                     is not activated. The default value is zero.                    Vendor Specific Extensions                                                                  Optional vendor specific extensions.                            ______________________________________                                    

A Termination System Information ("TSI") message is transmitted by CMTS12 at periodic intervals (e.g., every 2 seconds) to report CMTS 12information to CM 16 whether or not telephony return is used. The TSImessage is transmitted as a MAC 44 management message. The TSI providesa CMTS 12 boot record in a downstream channel to CM 16 via cable network14. Information in the TSI is used by CM 16 to obtain information aboutthe status of CMTS 12. The TSI message has a MAC 44 management typevalue of TRI₋₋ TSI.

FIG. 4 is a block diagram of a TSI message structure 76. TSI messagestructure 76 includes a MAC 44 management header 78, a downstreamchannel IP address 80, a registration IP address 82, a CMTS 12 boot time84, a downstream channel identifier 86, an epoch time 88 and vendorspecific TLV encoded data 90.

A description of the fields of TSI message 76 are shown in Table 2.However, more or fewer fields could also be used in TSI message 76.

                  TABLE 2                                                         ______________________________________                                        TSI 76 Parameter                                                                              Description                                                   ______________________________________                                        Downstream Channel                                                                            This field contains an IP 54 address of                       IP Address 80   CMTS 12 available on the downstream                                           channel this message arrived on.                              Registration IP Address 82                                                                    This field contains an IP 54 address                                          CM 16 sends its registration request                                          messages to. This address MAY be                                              the same as the Downstream Channel                                            IP 54 address.                                                CMTS Boot Time 84                                                                             Specifies an absolute-time of a CMTS                                          12 recorded epoch. The clock setting                                          for this epoch uses the current clock                                         time with an unspecified accuracy.                                            Time is represented as a 32 bit binary                                        number.                                                       Downstream Channel ID 86                                                                      A downstream channel on which this                                            message has been transmitted. This                                            identifier is arbitrarily chosen by CMTS                                      12 and is unique within the MAC 44                                            layer.                                                        Epoch 88        An integer value that is incremented                                          each time CMTS 12 is either re-                                               initialized or performs address or                                            routing table flush.                                          Vendor Specific Extensions 90                                                                 Optional vendor extensions may be                                             added as TLV encoded data.                                    ______________________________________                                    

After receiving TCD 70 message and TSI message 76, CM 16 continues toestablish access to data network 28 (and resources on the network) byfirst dialing into TRAC 24 and establishing a telephony PPP 50 session.Upon the completion of a successful PPP 50 connection, CM 16 performsPPP Link Control Protocol ("LCP") negotiation with TRAC 24. Once LCPnegotiation is complete, CM 16 requests Internet Protocol ControlProtocol ("IPCP") address negotiation. For more information on IPCP seeRFC-1332 incorporated herein by reference. During IPCP negotiation, CM16 negotiates an IP 54 address with TRAC 24 for sending IP 54 datapacket responses back to data network 28 via TRAC 24.

When CM 16 has established an IP 54 link to TRAC 24, it begins"upstream" communications to CMTS 12 via DHCP layer 66 to complete avirtual data connection by attempting to discover network hostinterfaces available on CMTS 12 (e.g., IP 54 host interfaces for avirtual IP 54 connection). The virtual data connection allows CM 16 toreceive data from data network 28 via CMTS 12 and cable network 14, andsend return data to data network 28 via TRAC 24 and PSTN 22. CM 16 mustfirst determine an address of a host interface (e.g., an IP 54interface) available on CMTS 12 that can be used by data network 28 tosend data to CM 16. However, CM 16 has only a downstream connection fromCMTS 12 and has to obtain a connection address to data network 28 usingan upstream connection to TRAC 24.

Addressing network host interfaces in the data-over-cable system via thecable modem

FIG. 5 is a flow diagram illustrating a method 92 for addressing networkhost interfaces in a data-over-cable system with telephony return via acable modem. Method 92 allows a cable modem to establish a virtual dataconnection to a data network. In method 92, multiple network devices areconnected to a first network with a downstream connection of a firstconnection type, and connected to a second network with an upstreamconnection of a second connection type. The first and second networksare connected to a third network with a third connection type.

At step 94, a selection input is received on a first network device fromthe first network over the downstream connection. The selection inputincludes a first connection address allowing the first network device tocommunicate with the first network via upstream connection to the secondnetwork. At step 96, a first message of a first type for a firstprotocol is created on the first network device having the firstconnection address from the selection input in a first message field.The first message is used to request a network host interface address onthe first network. The first connection address allows the first networkdevice to have the first message with the first message type forwardedto network host interfaces available on the first network via theupstream connection to the second network.

At step 98, the first network device sends the first message over theupstream connection to the second network. The second network uses thefirst address field in the first message to forward the first message toone or more network host interfaces available on first network at step100. Network host interfaces available on the first network that canprovide the services requested in first message send a second messagewith a second message type with a second connection address in a secondmessage field to the first network at step 102. The second connectionaddress allows the first network device to receive data packets from thethird network via a network host interface available on the firstnetwork. The first network forwards one or more second messages on thedownstream connection to the first network device at step 104.

The first network device selects a second connection address from one ofthe second messages from one of the one or more network host interfacesavailable on the first network at step 106 and establishes a virtualconnection from the third network to the first network device using thesecond connection address for the selected network host interface.

The virtual connection includes receiving data on the first network hostinterface on the first network from the third network and sending thedata over the downstream connection to the first network device. Thefirst network device sends data responses back to the third network overthe upstream connection to the second network, which forwards the datato the appropriate destination on the third network.

In one embodiment of the present invention, the data-over-cable systemis data-over-cable system 10, the first network device is CM 16, thefirst network is cable television network 14, the downstream connectionis a cable television connection. The second network is PSTN 22, theupstream connection is a telephony connection, the third network is datanetwork 28 (e.g., the Internet or an intranet) and the third type ofconnection is an IP 54 connection. The first and second connectionaddresses are IP 54 addresses. However, the present invention is notlimited to the network components and addresses described. Method 92allows CM 16 to determine an IP 54 network host interface addressavailable on CMTS 12 to receive IP 54 data packets from data network 28,thereby establishing a virtual IP 54 connection with data network 28.

After addressing network host interfaces using method 92, an exemplarydata path through cable system 10 is illustrated in Table 3. Howeverother data paths could also be used and the present invention is notlimited to the data paths shown in Table 3. For example, CM 16 may senddata upstream back through cable network 14 (e.g., CM 16 to cablenetwork 14 to CMTS 12) and not use PSTN 22 and the telephony returnupstream path.

                  TABLE 3                                                         ______________________________________                                        1.  An IP 54 datagram from data network 28 destined for CM 16 arrives             on CMTS-NSI 32 and enters CMTS 12.                                        2.  CMTS 12 encodes the IP 54 datagram in a cable data frame, passes              it to MAC 44 and transmits it "downstream" to RF interface 40 on              CM 16 via cable network 14.                                               3.  CM 16 recognizes the encoded IP 54 datagram in MAC layer 44                   received via RF interface 40.                                             4.  CM 16 responds to the cable data frame and encapsulates a response            IP 54 datagram in a PPP 50 frame and transmits it "upstream" with             modem interface 48 via PSTN 22 to TRAC 24.                                5.  TRAC 24 decodes the IP 54 datagram and forwards it via                        TRAC-NSI 30 to a destination on data network 28.                          ______________________________________                                    

Dynamic network host configuration on data-over-cable system

As was illustrated in FIG. 2, CM 16 includes a Dynamic HostConfiguration Protocol ("DHCP") layer 66, hereinafter DHCP 66. DHCP 66is used to provide configuration parameters to hosts on a network (e.g.,an IP 54 network). DHCP 66 consists of two components: a protocol fordelivering host-specific configuration parameters from a DHCP 66 serverto a host and a mechanism for allocation of network host addresses tohosts. DHCP 66 is built on a client-server model, where designated DHCP66 servers allocate network host addresses and deliver configurationparameters to dynamically configured network host clients.

FIG. 6 is a block diagram illustrating a DHCP 66 message structure 108.The format of DHCP 66 messages is based on the format of BOOTstrapProtocol ("BOOTP") messages described in RFC-951 and RFC-1542incorporated herein by reference. From a network host client's point ofview, DHCP 66 is an extension of the BOOTP mechanism. This behaviorallows existing BOOTP clients to interoperate with DHCP 66 serverswithout requiring any change to network host the clients' BOOTPinitialization software. DHCP 66 provides persistent storage of networkparameters for network host clients.

To capture BOOTP relay agent behavior described as part of the BOOTPspecification and to allow interoperability of existing BOOTP clientswith DHCP 66 servers, DHCP 66 uses a BOOTP message format. Using BOOTPrelaying agents eliminates the necessity of having a DHCP 66 server oneach physical network segment.

DHCP 66 message structure 108 includes an operation code field 110("op"), a hardware address type field 112 ("htype"), a hardware addresslength field 114 ("hlen"), a number of hops field 116 ("hops"), atransaction identifier field 118 ("xid"), a seconds elapsed time field120 ("secs"), a flags field 122 ("flags"), a client IP address field 124("ciaddr"), a your IP address field 126 ("yiaddr"), a server IP addressfield 128 ("siaddr"), a gateway/relay agent IP address field 130("giaddr"), a client hardware address field 132 ("chaddr"), an optionalserver name field 134 ("sname"), a boot file name 136 ("file") and anoptional parameters field 138 ("options"). Descriptions for DHCP 66message 108 fields are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        DCHP 66                                                                       Parameter    Description                                                      ______________________________________                                        OP 110       Message op code/message type.                                                 1 BOOTREQUEST, 2 = BOOTREPLY.                                    HTYPE 112    Hardware address type (e.g., `1` = 10                                         Mps Ethernet).                                                   HLEN 114     Hardware address length (e.g. `6` for 10                                      Mbps Ethernet).                                                  HOPS 116     Client sets to zero, optionally used by                                       relay-agents when booting via a relay-                                        agent.                                                           XID 118      Transaction ID, a random number                                               chosen by the client, used by the client                                      and server to associate messages and                                          responses between a client and a                                              server.                                                          SECS 120     Filled in by client, seconds elapsed                                          since client started trying to boot.                             FLAGS 122    Flags including a BROADCAST bit.                                 CIADDR 124   Client IP address; filled in by client in                                     DHCPREQUEST if verifying previously                                           allocated configuration parameters.                              YIADDR 126   `Your`(client) IP address.                                       SIADDR 128   IP 54 address of next server to use in                                        bootstrap; returned in DHCPOFFER,                                             DHCPACK and DHCPNAK by server.                                   GIADDR 130   Gateway relay agent IP 54 address,                                            used in booting via a relay-agent.                               CHADDR       Client hardware address (e.g., MAC                               132          layer 44 address).                                               SNAME 134    Optional server host name, null                                               terminated string.                                               FILE 136     Boot file name, terminated by a null                                          string.                                                          OPTIONS      Optional parameters.                                             138                                                                           ______________________________________                                    

The DHCP 66 message structure shown in FIG. 6 is used to discover IP 54and other network host interfaces in data-over-cable system 10. Anetwork host client (e.g., CM 16) uses DHCP 66 to acquire or verify anIP 54 address and network parameters whenever the network parameters mayhave changed. Table 5 illustrates a typical use of the DHCP 66 protocolto discover a network host interface from a network host client.

                  TABLE 5                                                         ______________________________________                                        1.  A network host client broadcasts a DHCP 66 discover message on                its local physical subnet. The DHCP 66 discover message may                   include options that suggest values for a network host interface              address. BOOTP relay agents may pass the message on to DHCP 66                servers not on the same physical subnet.                                  2.  DHCP servers may respond with a DHCPOFFER message that                        includes an available network address in the `yiaddr` field                   (and other configuration parameters in DHCP 66 options) from a                network host interface. DHCP 66 servers unicasts the DHCPOFFER                message to the network host client (using the DHCP/BOOTP relay                agent if necessary) if possible, or may broadcast the message to a            broadcast address (preferably 255.255.255.255) on the client's                subnet.                                                                   3.  The network host client receives one or more DHCPOFFER messages               from one or more DHCP 66 servers. The network host client may                 choose to wait for multiple responses.                                    4.  The network host client chooses one DHCP 66 server with an                    associated network host interface from which to request                       configuration                                                                 parameters, based on the configuration parameters offered in the              DHCPOFFER messages.                                                       ______________________________________                                    

Discovering network host interfaces in the data-over-cable system

The DHCP discovery process illustrated in table 5 will not work indata-over-cable system 10. CM 16 has only a downstream connection fromCMTS 12, which includes DHCP 66 servers, associated with network hostinterfaces available on CMTS 12. In an illustrative embodiment of thepresent invention, CM 16 discovers network host interfaces via TRAC 24and PSTN 22 on an upstream connection.

The DHCP 66 addressing process shown in Table 5 was not originallyintended to discover network host interfaces in data-over-cable system10. CMTS 12 has DHCP 66 servers associated with network host interfaces(e.g., IP interfaces), but CM 16 only has as downstream connection fromCMTS 12. CM 16 has an upstream connection to TRAC 24, which has a DHCP66 layer. However, TRAC 24 does not have DHCP 66 servers, or directaccess to network host interfaces on CMTS 12.

FIGS. 7A and 7B are a flow diagram illustrating a method 140 fordiscovering network host interfaces in data-over-cable system 10. WhenCM 16 has established an IP 54 link to TRAC 24, it begins communicationswith CMTS 12 via DHCP 66 to complete a virtual IP 54 connection withdata network 28. However, to discover what IP 54 host interfaces mightbe available on

CMTS 12, CM 16 has to communicate with CMTS 12 via PSTN 22 and TRAC 24since CM 16 only has a "downstream" cable channel from CMTS 12.

At step 142 in FIG. 7A, after receiving a TSI message 76 from CMTS 12 ona downstream connection, CM 16 generates a DHCP discover("DHCPDISCOVER") message and sends it upstream via PSTN 22 to TRAC 22 todiscover what IP 54 interfaces are available on CMTS 12. The fields ofthe DHCP discover message are set as illustrated in Table 6. However,other field settings may also be used.

                  TABLE 6                                                         ______________________________________                                        DHCP 66                                                                       Parameter   Description                                                       ______________________________________                                        OP 110      Set to BOOTREQUEST.                                               HTYPE 112   Set to network type (e.g., one for 10 Mbps                                    Ethernet).                                                        HLEN 114    Set to network length (e.g., six for 10 Mbps                                  Ethernet)                                                         HOPS 116    Set to zero.                                                      FLAGS 118   Set BROADCAST bit to zero.                                        CIADDR 124  If CM 16 has previously been assigned an IP                                   54 address, the IP 54 address is placed in this                               field. If CM 16 has previously been assigned                                  an IP 54 address by DHCP 66, and also has                                     been assigned an address via IPCP, CM 16                                      places the DHCP 66 IP 54 address in this                                      field.                                                            GIADDR 130  CM 16 places the Downstream Channel IP 54                                     address 80 of CMTS 12 obtained in TSI                                         message 76 on a cable downstream channel                                      in this field.                                                    CHADDR 132  CM 16 places its 48-bit MAC 44 LAN address                                    in this field.                                                    ______________________________________                                    

The DHCPDISCOVER message is used to "discover" the existence of one ormore IP 54 host interfaces available on CMTS 12. DHCP 66 giaddr-field130 (FIG. 6) includes the downstream channel IP address 80 of CMTS 12obtained in TSI message 76 (e.g., the first message field from step 96of method 92). Using the downstream channel IP address 80 of CMTS 12obtained in TSI message 76 allows the DHCPDISCOVER message to beforwarded by TRAC 24 to DHCP 66 servers (i.e., protocol servers)associated with network host interfaces available on CMTS 12. If DHCP 66giaddr-field 130 (FIG. 6) in a DHCP message from a DHCP 66 client isnon-zero, the DHCP 66 server sends any return messages to a DHCP 66server port on a DHCP 66 relaying agent (e.g., CMTS 12) whose addressappears in DHCP 66 giaddr-field 130.

In a typical DHCP 66 discovery process the DHCP 66 giaddr-field 130 isset to zero. If DHCP 66 giaddr-field 130 is zero, the DHCP 66 client ison the same subnet as the DHCP 66 server, and the DHCP 66 server sendsany return messages to either the DHCP 66 client's network address, ifthat address was supplied in DHCP 66 ciaddr-field 124 (FIG. 6), or to aclient's hardware address specified in DHCP 66 chaddr-field 132 (FIG. 6)or to a local subnet broadcast address (e.g., 255.255.255.255).

At step 144, a DHCP 66 layer on TRAC 24 broadcasts the DHCPDISCOVERmessage on its local network leaving DHCP 66 giaddr-field 130 intactsince it already contains a non-zero value. TRAC's 24 local networkincludes connections to one or more DHCP 66 proxies (i.e., network hostinterface proxies). The DHCP 66 proxies accept DHCP 66 messagesoriginally from CM 16 destined for DHCP 66 servers connected to networkhost interfaces available on CMTS 12 since TRAC 24 has no direct accessto DCHP 66 servers associated with network host interfaces available onCMTS 12. DHCP 66 proxies are not used in a typical DHCP 66 discoveryprocess.

One or more DHCP 66 proxies on TRAC's 24 local network recognizes theDHCPDISCOVER message and forwards it to one or more DHCP 66 serversassociated with network host interfaces (e.g., IP 54 interfaces)available on CMTS 12 at step 146. Since DHCP 66 giaddr-field 130 (FIG.6) in the DHCPDISCOVER message sent by CM 16 is already non-zero (i.e.,contains the downstream IP address of CMTS 12), the DHCP 66 proxies alsoleave DHCP 66 giaddr-field 130 intact.

One or more DHCP 66 servers for network host interfaces (e.g., IP 54interfaces) available on CMTS 12 receive the DHCPDISCOVER message andgenerate a DHCP 66 offer message ("DHCPOFFER") at step 148. The DHCP 66offer message is an offer of configuration parameters sent from networkhost interfaces to DHCP 66 servers and back to a network host client(e.g., CM 16) in response to a DHCPDISCOVER message. The DHCP 66 offermessage is sent with the message fields set as illustrated in Table 7.However, other field settings can also be used. DHCP 66 yiaddr-field 126(e.g., second message field from step 102 of method 92) contains an IP54 address for a network host interface available on CMTS 12 and usedfor receiving data packets from data network 28.

                  TABLE 7                                                         ______________________________________                                        DHCP 66 Parameter                                                                             Description                                                   ______________________________________                                        FLAGS 122       BROADCAST bit set to zero.                                    YIADDR 126      IP 54 address from a network                                                  host interface to allow CM 16 to                                              receive data from data network                                                28 via a network host interface                                               available on CMTS 12.                                         SIADDR 128      An IP 54 address for a TFTP 64                                                server to download configuration                                              information for an interface host.                            CHADDR 132      MAC 44 address of CM 16.                                      SNAME 134       Optional DHCP 66 server                                                       identifier with an interface host.                            FILE 136        A TFTP 64 configuration file                                                  name for CM 16.                                               ______________________________________                                    

DHCP 66 servers send the DHCPOFFER message to the address specified in66 giaddr-field 130 (i.e., CMTS 12) from the DHCPDISCOVER message ifassociated network host interfaces (e.g., IP 54 interfaces) can offerthe requested service (e.g., IP 54 service) to CM 16. The DHCPDISOVERmessage DHCP 66 giaddr-field 130 contains a downstream channel IPaddress 80 of CMTS 12 that was received by CM 16 in TSI message 76. Thisallows CMTS 12 to receive the DHCPOFFER messages from the DHCP 66servers and send them to CM 16 via a downstream channel on cable network14.

At step 150 in FIG. 7B, CMTS 12 receives one or more DHCPOFFER messagesfrom one or more DHCP 66 servers associated with the network hostinterfaces (e.g., IP 54 interfaces). CMTS 12 examines DHCP 66yiaddr-field 126 and DHCP 66 chaddr-field 132 in the DHCPOFFER messagesand sends the DHCPOFFER messages to CM 16 via cable network 14. DHCP 66yiaddr-field 126 contains an IP 54 address for a network host IP 54interface available on CMTS 12 and used for receiving IP 54 data packetsfrom data network 28. DHCP 66 chaddr-field 132 contains the MAC 44 layeraddress for CM 16 on a downstream cable channel from CMTS 12 via cablenetwork 14. CMTS 12 knows the location of CM 16 since it sent CM 16 aMAC 44 layer address in one or more initialization messages (e.g., TSImessage 76).

If a BROADCAST bit in flags field 124 is set to one, CMTS 12 sends theDHCPOFFER messages to a broadcast IP 54 address (e.g., 255.255.255.255)instead of the address specified in DHCP 66 yiaddr-field 126. DHCP 66chaddr-field 132 is still used to determine that MAC 44 layer address.If the BROADCAST bit in DHCP 66 flags field 122 is set, CMTS 12 does notupdate internal address or routing tables based upon DHCP 66yiaddr-field 126 and DHCP 66 chaddr-field 132 pair when a broadcastmessage is sent.

At step 152, CM 16 receives one or more DHCPOFFER messages from CMTS 12via cable network 14 on a downstream connection. At step 154, CM 16selects an offer for IP 54 service from one of the network hostinterfaces (e.g., an IP interfaces 54) available on CMTS 12 thatresponded to the DHCPDISOVER message sent at step 142 in FIG. 7A andestablishes a virtual IP 54 connection. The selected DHCPOFFER messagecontains a network host interface address (e.g., IP 54 address) in DHCP66 yiaddr-field 126 (FIG. 6). A cable modem acknowledges the selectednetwork host interface with DHCP 66 message sequence explained below.

After selecting and acknowledging a network host interface, CM 16 hasdiscovered an IP 54 interface address available on CMTS 12 forcompleting a virtual IP 54 connection with data network 28.Acknowledging a network host interface is explained below. The virtualIP 54 connection allows IP 54 data from data network 28 to be sent toCMTS 12 which forwards the IP 54 packets to CM 16 on a downstreamchannel via cable network 14. CM 16 sends response IP 54 packets back todata network 28 via PSTN 22 and TRAC 24.

FIG. 8 is a block diagram illustrating a data-over-cable system 156 forthe method illustrated in FIGS. 7A and 7B. Data-over-cable system 156includes DHCP 66 proxies 158, DHCP 66 servers 160 and associated NetworkHost Interfaces 162 available on CMTS 12. Multiple DHCP 66 proxies 158,DHCP 66 servers 160 and network host interfaces 162 are illustrated assingle boxes in FIG. 8. FIG. 8 also illustrates DHCP 66 proxies 158separate from TRAC 24. In one embodiment of the present invention, TRAC24 includes DHCP 66 proxy functionality and no separate DHCP 66 proxies158 are used. In such an embodiment, TRAC 24 forwards DHCP 66 messagesusing DHCP 66 giaddr-field 130 to DHCP 66 servers 160 available on CMTS12.

FIG. 9 is a block diagram illustrating a message flow 162 of method 140(FIGS. 7A and 7B).

Message flow 162 includes DHCP proxies 158 and DHCP servers 160illustrated in FIG. 8 Steps 142, 144, 146, 148, 150 and 154 of method140 (FIGS. 7A and 7B) are illustrated in FIG. 9. In one embodiment ofthe present invention, DHCP proxies 158 are not separate entities, butare included in TRAC 24. In such an embodiment, DHCP proxy services areprovided directly by TRAC 24.

Resolving addresses for network host interfaces

Since CM 16 receives multiple DHCPOFFER messages (Step 152 FIG. 7B) CM16 resolves and acknowledges one offer from a selected network hostinterface. FIGS. 10A and 10B are a flow diagram illustrating a method166 for resolving and acknowledging host addresses in a data-over-cablesystem. Method 166 includes a first network device that is connected toa first network with a downstream connection of a first connection type,and connected to a second network with an upstream connection of asecond connection type. The first and second networks are connected to athird network with a third connection type. In one embodiment of thepresent invention, the first network device is CM 16, the first networkis cable network 14, the second network is PSTN 22 and the third networkis data network 28 (e.g., the Internet). The downstream connection is acable television connection, the upstream connection is a telephonyconnection, and the third connection is an IP connection.

Turning to FIG. 10A, one or more first messages are received on thefirst network device from the first network on the downstream connectionat step 168. The one or more first messages are offers from one or morenetwork host interfaces available on the first network to provide thefirst network device a connection to the third network. The firstnetwork device selects one of the network host interfaces using messagefields in one of the one or more first messages at step 170. The firstnetwork device creates a second message with a second message type toaccept the offered services from a selected network host interface atstep 172. The second message includes a connection address for the firstnetwork in a first message field and an identifier to identify theselected network host interface in a second message field.

The first network device sends the second message over the upstreamconnection to the second network at step 174. The second network usesthe first message field in the second message to forward the secondmessage to the one or more network host interfaces available on firstnetwork at step 176.

A network host interface available on the first network identified insecond message field in the second message from the first network devicerecognizes an identifier for the network host interface at 178 in FIG.10B. The selected network host interface sends a third message with athird message type to the first network at step 180. The third messageis an acknowledgment for the first network device that the selectednetwork host interface received the second message from the firstnetwork device. The first network stores a connection address for theselected network interface in one or more tables on the first network atstep 182. The first network will forward data from the third network tothe first network device when it is received on the selected networkhost interface using the connection address in the one or more routingtables. The first network forwards the third message to the firstnetwork device on the downstream connection at step 184. The firstnetwork device receives the third message at step 186. The first networkand the first network device have the necessary addresses for a virtualconnection that allows data to be sent from the third network to anetwork host interface on the first network, and from the first networkover the downstream connection to the first network device. Method 166accomplishes resolving network interface hosts addresses from a cablemodem in a data-over-cable with telephony return.

Method 166 of the present invention is used in data-over-cable system 10with telephony return. However, the present invention is not limited todata-over-cable system 10 with telephony return and can be used indata-over-cable system 10 without telephony return by using an upstreamcable channel instead of an upstream telephony channel.

FIGS. 11A and 11B are a flow diagram illustrating a method 188 forresolving discovered host addresses in data-over-cable system 10 withtelephony return. At step 190 in FIG. 11A, CM 16 receives one or moreDHCPOFFER messages from one or more DHCP 66 servers associated with oneor more network host interfaces (e.g., at step 168 in method 166). Theone or more DHCPOFFER messages include DHCP 66 fields set as illustratedin Table 7 above. However, other field settings could also be used. Atstep 192, CM 16 selects one of the DHCPOFFER messages (see also, step170 in method 166). At step 194, CM 16 creates a DHCP 66 request message("DHCPREQUEST") message to request the services offered by a networkhost interface selected at step 192. The fields of the DHCP requestmessage are set as illustrated in Table 8. However, other field settingsmay also be used.

                  TABLE 8                                                         ______________________________________                                        DHCP 66                                                                       Parameter   Description                                                       ______________________________________                                        OP 110      Set to BOOTREQUEST.                                               HTYPE 112   Set to network type (e.g., one for 10 Mbps                                    Ethernet).                                                        HLEN 114    Set to network length (e.g., six for 10 Mbps                                  Ethernet)                                                         HOPS 116    Set to zero.                                                      FLAGS 118   Set BROADCAST bit to zero.                                        CIADDR 124  If CM 16 has previously been assigned an IP                                   address, the IP address is placed in this field.                              If CM 16 has previously been assigned an IP                                   address by DHCP 66, and also has been                                         assigned an address via IPCP, CM 16 places                                    the DHCP 66 IP 54 address in this field.                          YIADDR 126  IP 54 address sent from the selected network                                  interface host in DCHPOFFER message                               GIADDR 130  CM 16 places the Downstream Channel IP 54                                     address 80 CMTS 12 obtained in TSI                                            message 76 on a cable downstream channel                                      in this field.                                                    CHADDR 132  CM 16 places its 48-bit MAC 44 LAN address                                    in this field.                                                    SNAME 134   DHCP 66 server identifier for the selected                                    network interface host                                            ______________________________________                                    

The DHCPREQUEST message is used to "request" services from the selectedIP 54 host interface available on CMTS 12 using a DHCP 66 serverassociated with the selected network host interface. DHCP 66giaddr-field 130 (FIG. 6) includes the downstream channel IP address 80for CMTS 12 obtained in TSI message 76 (e.g., the first message-fieldfrom step 172 of method 166). Putting the downstream channel IP address80 obtained in TSI message 76 allows the DHCPREQUEST message to beforwarded by TRAC 24 to DCHP 66 servers associated with network hostinterfaces available on CMTS 12. DHCP 66 giaddr-field 126 contains anidentifier (second message field, step 172 in method 166) DHCP 66sname-field 134 contains a DHCP 66 server identifier associated with theselected network host interface.

If DHCP 66 giaddr-field 130 in a DHCP message from a DHCP 66 client isnon-zero, a DHCP 66 server sends any return messages to a DHCP 66 serverport on a DHCP 66 relaying agent (e.g., CMTS 12) whose address appearsin DHCP 66 giaddr-field 130. If DHCP 66 giaddr-field 130 is zero, theDHCP 66 client is on the same subnet as the DHCP 66 server, and the DHCP66 server sends any return messages to either the DHCP 66 client'snetwork address, if that address was supplied in DHCP 66 ciaddr-field124, or to the client's hardware address specified in DHCP 66chaddr-field 132 or to the local subnet broadcast address.

Returning to FIG. 11A at step 196, CM 16 sends the DHCPREQUEST messageon the upstream connection to TRAC 24 via PSTN 22. At step 198, a DHCP66 layer on TRAC 24 broadcasts the DHCPREQUEST message on its localnetwork leaving DHCP 66 giaddr-field 130 intact since it alreadycontains a non-zero value. TRACts 24 local network includes connectionsto one or more DHCP 66 proxies. The DHCP 66 proxies accept DHCP 66messages originally from CM 16 destined for DHCP 66 servers associatedwith network host interfaces available on CMTS 12. In another embodimentof the present invention, TRAC 24 provides the DHCP 66 proxyfunctionality, and no separate DHCP 66 proxies are used.

The one or more DHCP 66 proxies on TRAC's 24 local network messageforwards the DHCPOFFER to one or more of the DHCP 66 servers associatedwith network host interfaces (e.g., IP 54 interfaces) available on CMTS12 at step 200 in FIG. 11B. Since DHCP 66 giaddr-field 130 in theDHCPDISCOVER message sent by CM 16 is already non-zero (i.e., containsthe downstream IP address of CMTS 12), the DHCP 66 proxies leave DHCP 66giaddr-field 130 intact.

One or more DHCP 66 servers for the selected network host interfaces(e.g., IP 54 interface) available on CMTS 12 receives the DHCPOFFERmessage at step 202. A selected DHCP 66 server recognizes a DHCP 66server identifier in DHCP 66 sname-field 134 or the IP 54 address thatwas sent in the DCHPOFFER message in the DHCP 66 yiaddr-field 126 fromthe DHCPREQUST message as being for the selected DHCP 66 server.

The selected DHCP 66 server associated with network host interfaceselected by CM 16 in the DHCPREQUEST message creates and sends a DCHP 66acknowledgment message ("DHCPACK") to CMTS 12 at step 204. The DHCPACKmessage is sent with the message fields set as illustrated in Table 9.However, other field settings can also be used. DHCP 66 yiaddr-fieldagain contains the IP 54 address for the selected network host interfaceavailable on CMTS 12 for receiving data packets from data network 28.

                  TABLE 9                                                         ______________________________________                                        DHCP 66 Parameter                                                                            Description                                                    ______________________________________                                        FLAGS 122      Set a BROADCAST bit to zero.                                   YIADDR 126     IP 54 address for the selected                                                network host interface to allow                                               CM 16 to receive data from data                                               network 28.                                                    SIADDR 128     An IP 54 address for a TFTP 64                                                server to download configuration                                              information for an interface host.                             CHADDR 132     MAC 44 address of CM 16.                                       SNAME 134      DHCP 66 server identifier                                                     associated with the selected                                                  network host interface.                                        FILE 136       A configuration file name for an                                              network interface host.                                        ______________________________________                                    

The selected DHCP 66 server sends the DHCACK message to the addressspecified in DHCP 66 giaddr-field 130 from the DHCPREQUEST message to CM16 to verify the selected network host interface (e.g., IP 54 interface)will offer the requested service (e.g., IP 54 service).

At step 206, CMTS 12 receives the DHCPACK message from the selected DHCP66 server associated with the selected network host interface IP 54address(e.g., IP 54 interface). CMTS 12 examines DHCP 66 yiaddr-field126 and DHCP 66 chaddr-field 132 in the DHCPOFFER messages. DHCP 66yiaddr-field 126 contains an IP 54 address for a network host IP 54interface available on CMTS 12 and used for receiving IP 54 data packetsfrom data network 28 for CM 16. DHCP 66 chaddr-field 132 contains theMAC 44 layer address for CM 16 on a downstream cable channel from CMTS12 via cable network 14.

CMTS 12 updates an Address Resolution Protocol ("ARP") table and otherrouting tables on CMTS 12 to reflect the addresses in DHCP 66yiaddr-field 126 and DHCP 66 chaddr-field 132 at step 208. As is knownin the art, ARP allows a gateway such as CMTS 12 to forward anydatagrams from a data network such as data network 28 it receives forhosts such as CM 16. ARP is defined in RFC-826, incorporated herein byreference.

CMTS 12 stores a pair of network address values in the ARP table, the IP54 address of the selected network host interface from DHCP 66yiaddr-field 126 and a Network Point of Attachment ("NPA") address. Inan illustrative embodiment of the present invention, The NPA address isa MAC 44 layer address for CM 16 via a downstream cable channel. TheIP/NPA address pair are stored in local routing tables with the IPINPAaddresses of hosts (e.g., CMs 16) that are attached to cable network 14.

At step 210, CMTS 12 sends the DHCPACK message to CM 16 via cablenetwork 14. At step 212, CM 16 receives the DHCPACK message, and alongwith CMTS 12 has addresses for a virtual connection between data network28 and CM 16. When data packets arrive on the IP 54 address for theselected host interface they are sent to CMTS 12 and CMTS 12 forwardsthem using a NPA (i.e., MAC 44 address) from the routing tables on adownstream channel via cable network 14 to CM 16.

If a BROADCAST bit in flags field 124 is set to one in the DHCPACK, CMTS12 sends the DHCPACK messages to a broadcast IP 54 address (e.g.,255.255.255.255). DHCP 66 chaddr-field 132 is still used to determinethat MAC layer address. If the BROADCAST bit in flags field 122 is set,CMTS 12 does not update the ARP table or offer routing tables based uponDHCP 66 yiaddr-field 126 and DHCP 66 chaddr-field 132 pair when abroadcast message is sent.

FIG. 12 is a block diagram illustrating the message flow 214 of themethod 188 illustrated in FIGS. 11A and 11B. Message flow 214 includesDHCP proxies 158 and DHCP servers 160 illustrated in FIG. 8. Methodsteps 194, 196, 198, 204, 208, 210 and 212 of method 188 (FIGS. 11A and11B) are illustrated in FIG. 12. In one embodiment of the presentinvention, DHCP proxies 158 are not separate entities, but are includedin TRAC 24. In such an embodiment, DHCP proxy services are provideddirectly by TRAC 24.

After method 188, CMTS 12 has a valid IP/MAC address pair in one or moreaddress routing tables including an ARP table to forward IP 54 datapackets from data network 28 to CM 16, thereby creating a virtual IP 54data path to/from CM 16 as was illustrated in method 92 (FIG. 5) andTable 3. CM 16 has necessary parameters to proceed to the next phase ofinitialization, a download of a configuration file via TFTP 64. Once CM16 has received the configuration file and has been initialized, itregisters with CMTS 12 and is ready to receive data from data network14.

In the event that CM 16 is not compatible with the configuration of thenetwork host interface received in the DHCPACK message, CM 16 maygenerate a DHCP 66 decline message ("DHCPDECLINE") and transmit it toTRAC 24 via PSTN 22. A DHCP 66 layer in TRAC 24 forwards the DHCPDECLINEmessage to CMTS 12. Upon seeing a DHCPDECLINE message, CMTS 12 flushesits ARP tables and routing tables to remove the now invalid IP/MACpairing. If an IP 54 address for a network host interface is returnedthat is different from the IP 54 address sent by CM 16 in theDCHCPREQUEST message, CM 16 uses the IP 54 address it receives in theDHCPACK message as the IP 54 address of the selected network hostinterface for receiving data from data network 28.

The present invention is described with respect to, but is not limitedto a data-over-cable-system with telephony return. Method 188 can alsobe used with a cable modem that has a two-way connection (i.e., upstreamand downstream) to cable network 14 and CMTS 12. In adata-over-cable-system without telephony return, CM 16 would broadcastthe DHCPREQUEST message to one or more DHCP 66 servers associated withone or more network host interfaces available on CMTS 12 using anupstream connection on data network 14 including the IP 54 address ofCMTS 12 in DHCP 66 giaddr-field 130. Method 188 accomplishes resolvingaddresses for network interface hosts from a cable modem in adata-over-cable with or without telephony return, and without extensionsto the existing DHCP protocol.

CPE initialization in a data-over-cable system

CPE 18 also uses DHCP 66 to generate requests to obtain IP 54 addressesto allow CPE 18 to also receive data from data network 28 via CM 16. Inan illustrative embodiment of the present invention, CM 16 functions asa standard BOOTP relay agent/DHCP Proxy 158 to facilitate CPE's 18access to DHCP 66 server 160. FIGS. 13A and 13B are a flow diagramillustrating a method 216 for obtaining addresses for customer premiseequipment. CM 16 and CMTS 12 use information from method 214 toconstruct IP 54 routing and ARP table entries for network hostinterfaces 162 providing data to CMCI 20 and to CPE 18.

Method 216 in FIGS. 13A and 13B includes a data-over-cable system withtelephony return and first network device with a second network devicefor connecting the first network device to a first network with adownstream connection of a first connection type, and for connecting toa second network with an upstream connection of a second connectiontype. The first and second networks are connected to a third networkwith a third connection type.

In one embodiment of the present invention, data-over-cable system withtelephony return is data-over-cable system 10 with the first networkdevice CPE 18 and the second network device CM 16. The first network iscable television network 14, the downstream connection is a cabletelevision connection, the second network is PSTN 22, the upstreamconnection is a telephony connection, the third network is data network28 (e.g., the Internet or an intranet) and the third type of connectionis an IP 54 connection. However, the present invention is not limited tothe network components described and other network components may alsobe used. Method 216 allows CPE 18 to determine an IP 54 network hostinterface address available on CMTS 12 to receive IP 54 data packetsfrom data network 54, thereby establishing a virtual IP 54 connectionwith data network 28 via CM 16.

Returning to FIG. 13A at step 218, a first message of a first type(e.g., a DHCP 66 discover message) with a first message field for afirst connection is created on the first network device. The firstmessage is used to discover a network host interface address on thefirst network to allow a virtual connection to the third network.

At step 220, the first network device sends the first message to thesecond network device. The second network device checks the firstmessage field at step 222. If the first message field is zero, thesecond network device puts its own connection address into the firstmessage field at step 224. The second network device connection addressallows the messages from network host interfaces on the first network toreturn messages to the second network device attached to the firstnetwork device. If the first message field is non-zero, the secondnetwork device does not alter the first message field since there couldbe a relay agent attached to the first network device that may set thefirst connection address field.

At step 226, the second network device forwards the first message to aconnection address over the upstream connection to the second network.In one embodiment of the present invention, the connection address is anIP broadcast address (e.g., 255.255.255.255). However, other connectionaddresses can also be used.

The second network uses the first connection address in the firstmessage field in the first message to forward the first message to oneor more network host interfaces (e.g., IP 54 network host interfaces)available on first network at step 228. One or more network hostinterfaces available on the first network that can provide the servicesrequested in first message send a second message with a second messagetype with a second connection address in a second message field to thefirst network at step 230 in FIG. 13B. The second connection addressallows the first network device to receive data packets from the thirdnetwork via a network host interface on the first network. The firstnetwork forwards the one or more second messages on the downstreamconnection to the second network device at step 232. The second networkdevice forwards the one or more second messages to the first networkdevice at step 234. The first network device selects one of the one ormore network host interfaces on the first network using the one or moresecond messages at step 236. This allows a virtual connection to beestablished between the third network and the first network device viathe selected network host interface on the first network and the secondnetwork device.

FIGS. 14A and 14B are a flow diagram illustrating a method 240 forresolving addresses for the network host interface selected by a firstnetwork device to create a virtual connection to the third network.Turning to FIG. 14A, at step 240 one or more second messages arereceived with a second message type on the first network device from thesecond network device from the first network on a downstream connectionat step 242. The one or more second messages are offers from one or moreprotocol servers associated with one or more network host interfacesavailable on the first network to provide the first network device aconnection to the third network. The first network device selects one ofthe network host interfaces using one of the one or more second messagesat step 244. The first network device creates a third message with athird message type to accept the offered services from the selectednetwork host interface at step 246. The third message includes aconnection address for the first network in a first message field and anidentifier to identify the selected network host interface in a secondmessage field. At step 248, first network device equipment sends thethird message to the second network device.

The second network device sends the third message over the upstreamconnection to the second network at step 250. The second network usesthe first message field in the third message to forward the thirdmessage to the one or more network host interfaces available on firstnetwork at step 252.

A network host interface available on the first network identified insecond message field in the third message from the first network devicerecognizes an identifier for the selected network host interface at step254 in FIG. 14B. The selected network host interface sends a fourthmessage with a fourth message type to the first network at step 256. Thefourth message is an acknowledgment for the first network device thatthe selected network host interface received the third message. Thefourth message includes a second connection address in a third messagefield. The second connection address is a connection address for theselected network host interface. The first network stores the connectionaddress for the selected network interface from the third message in oneor more routing tables (e.g., an ARP table) on the first network at step258. The first network will forward data from the third network to thefirst network device via the second network device when it is receivedon the selected network host interface using the connection address fromthe third message field. The first network forwards the fourth messageto the second network device on the downstream connection at step 260.The second network device receives the fourth message and stores theconnection address from the third message field for the selected networkinterface in one or more routing tables on the second network device atstep 262. The connection address for the selected network interfaceallows the second network device to forward data from the third networksent by the selected network interface to the customer premiseequipment.

At step 264, the second network device forward the fourth message to thefirst network device. At step 266, the first network device establishesa virtual connection between the third network and the first networkdevice.

After step 266, the first network, the second network device and thefirst network device have the necessary connection addresses for avirtual connection that allows data to be sent from the third network toa network host interface on the first network, and from the firstnetwork over the downstream connection to the second network and then tothe first network device. In one embodiment of the present invention,method 240 accomplishes resolving network interface hosts addresses fromcustomer premise equipment with a cable modem in a data-over-cable withtelephony return without extensions to the existing DHCP protocol.

Methods 216 and 240 of the present invention are used in data-over-cablesystem 10 with telephony return with CM 16 and CPE 18. However, thepresent invention is not limited to data-over-cable system 10 withtelephony return and can be used in data-over-cable system 10 withouttelephony return by using an upstream cable channel instead of anupstream telephony channel.

FIGS. 15A and 15B are a flow diagram illustrating a method 268 foraddressing network host interfaces from CPE 18. At step 270 in FIG. 15A,CPE 18 generates a DHCPDISCOVER message broadcasts the DHCPDISCOVERmessage on its local network with the fields set as illustrated in Table6 above with addresses for CPE 18 instead of CM 16. However, more orfewer field could also be set. CM 16 receives the DHCPDISCOVER as astandard BOOTP relay agent at step 272. The DHCP DISCOVER message has aMAC 44 layer address for CPE 18 in DHCP 66 chaddr-field 132, which CM 16stores in one or more routing tables. As a BOOTP relay agent, the CM 16checks the DHCP 66 giaddr-field 130 (FIG. 6) at step 274. If DHCP 66giaddr-field 130 is set to zero, CM 16 put its IP 54 address into DHCP66 giaddr-field 130 at step 276.

If DHCP 66 giaddr-field 130 is non-zero, CM 16 does not alter DHCP 66giaddr-field 130 since there could be another BOOTP relay agent attachedto CPE 18 which may have already set DHCP 66 giaddr-field 130. Any BOOTPrelay agent attached to CPE 18 would have also have acquired its IP 54address from using a DCHP 66 discovery process (e.g., FIG. 12).

Returning to FIG. 15A, at step 278, CM 16 broadcasts the DHCPDISCOVERmessage to a broadcast address via PSTN 22 to TRAC 24. In one embodimentof the present invention, the broadcast address is an IP 54 broadcastaddress (e.g., 255.255.255.255). At step 280, one or more DHCP 66proxies 158 associated with TRAC 24, recognize the DHCPDISOVER message,and forward it to one or more DHCP 66 servers 160 associated with one ormore network host interfaces 162 available on CMTS 12. Since DHCP 66giaddr-field 130 is already non-zero, the DHCP proxies leave DHCP 66giaddr-field 130 intact. In another embodiment of the present invention,TRAC 24 includes DCHP 66 proxy 158 functionality and no separate DHCP 66proxies 158 are used.

At step 282 in FIG. 15B, the one or more DHCP servers 160 receive theDHCPDISCOVER message from one or more DHCP proxies, and generate one ormore DHCPOFFER messages to offer connection services for one or morenetwork host interfaces 162 available on CMTS 12 with the fields set asillustrated in Table 7. The one or more DHCP servers 160 send the one ormore DHCPOFFER messages to the address specified in DHCP 66 giaddr-field130 (e.g., CM 16 or a BOOTP relay agent on CPE 18), which is an IP 54address already contained in an ARP or other routing table in CMTS 12.Since CMTS 12 also functions as a relay agent for the one or more DHCPservers 160, the one or more DHCPOFFER messages are received on CMTS 12at step 284.

CMTS 12 examines DHCP 66 yiaddr-field 126 and DHCP 66 giaddr-field 130in the DHCPOFFER messages, and sends the DHCPOFFER messages down cablenetwork 14 to IP 54 address specified in the giaddr-field 130. The MAC44 address for CM 16 is obtained through a look-up of the hardwareaddress associated with DHCP 66 chaddr-field 130. If the BROADCAST bitin DHCP 66 flags-field 122 is set to one, CMTS 12 sends the DHCPOFFERmessage to a broadcast IP 54 address (e.g., 255.255.255.255), instead ofthe address specified in DHCP 66 yiaddr-field 126. CMTS 12 does notupdate its ARP or other routing tables based upon the broadcast DCHP 66yiaddr-field 126 DHCP 66 chaddr-field 132 address pair.

Returning to FIG. 15B, CM 16 receives the one or more DHCPOFFER messagesand forwards them to CPE 18 at step 286. CM 16 uses the MAC 44 addressspecified determined by DHCP 66 chaddr-field 132 look-up in its routingtables to find the address of CPE 18 even if the BROADCAST bit in DHCP66 flags-field 122 is set. At step 290, CPE 18 receives the one or moreDHCPOFFER messages from CM 16. At step 292, CPE 18 selects one of theDHCPOFFER messages to allow a virtual connection to be establishedbetween data network 28 and CPE 18. Method 266 accomplishes addressingnetwork interface hosts from CPE 18 in data-over-cable system 10 withoutextensions to the existing DHCP protocol.

FIGS. 16A and 16B are a flow diagram illustrating a method 294 forresolving network host interfaces from CPE 18. At step 296, CPE 18receives the one or more DHCPOFFER messages from one or more DHCP 66servers associated with one or more network host interface available onCMTS 12. At step 298, CPE 18 chooses one offer of services from aselected network host interface. At step 300, CPE 18 generates aDHCPREQUEST message with the fields set as illustrated in Table 8 abovewith addresses for CPE 18 instead of CM 16. However, more or fewerfields could also be set. At step 302, CPE 18 sends the DHCPREQUESTmessage to CM 16. At step 304, CM 16 forwards the message to TRAC 24 viaPSTN 22.

At step 306, a DHCP 66 layer on TRAC 24 broadcasts the DHCPREQUESTmessage on its local network leaving DHCP 66 giaddr-field 130 intactsince it already contains a non-zero value. TRAC's 24 local networkincludes connections to one or more DHCP 66 proxies. The DHCP 66 proxiesaccept DHCP 66 messages originally from CPE 18 destined for DHCP 66servers associated with network host interfaces available on CMTS 12. Inanother embodiment of the present invention, TRAC 24 provides the DHCP66 proxy functionality, and no separate DHCP 66 proxies are used.

One or more DHCP 66 proxies on TRAC's 24 local network recognize theDHCPOFFER message and forward it to one or more of the DHCP 66 serversassociated with network host interfaces (e.g., IP 54 interfaces)available on CMTS 12 at step 308 in FIG. 16B. Since DHCP 66 giaddr-field130 in the DHCPDISCOVER message sent by CPE 18 is already non-zero, theDHCP 66 proxies leave DHCP 66 giaddr-field 130 intact.

One or more DHCP 66 servers for the selected network host interfaces(e.g., IP 54 interface) available on CMTS 12 receive the DHCPOFFERmessage at step 310. A selected DHCP 66 server recognizes a DHCP 66server identifier in DHCP 66 sname-field 134 or the IP 54 address thatwas sent in the DCHPOFFER message in the DHCP 66 yiaddr-field 126 fromthe DHCPREQUST message for the selected DHCP 66 server.

The selected DHCP 66 server associated with network host interfaceselected by CPE 18 in the DHCPREQUEST message creates and sends a DCHPacknowledgment message ("DHCPACK") to CMTS 12 at step 312 using the DHCP66 giaddr-field 130. The DHCPACK message is sent with the message fieldsset as illustrated in Table 9. However, other field settings can also beused. DHCP 66 yiaddr-field contains the IP 54 address for the selectednetwork host interface available on CMTS 12 for receiving data packetsfrom data network 28 for CPE 18.

At step 314, CMTS 12 receives the DHCPACK message. CMTS 12 examines theDHCP 66 giaddr-field 130 and looks up that IP address in its ARP tablefor an associated MAC 44 address. This is a MAC 44 address for CM 16,which sent the DHCPREQUEST message from CPE 18. CMTS 12 uses the MAC 44address associated with the DHCP 66 giaddr-field 130 and the DHCP 66yiaddr-field 126 to update its routing and ARP tables reflecting thisaddress pairing at step 316. At step 318, CMTS 12 sends the DHCPACKmessage on a downstream channel on cable network 14 to the IP 54 and MAC44 addresses, respectively (i.e., to CM 16). If the BROADCAST bit in theDHCP 66 flags-field 122 is set to one, CMTS 12 sends the DHCPACK messageto a broadcast IP 54 address (e.g., 255.255.255.255), instead of theaddress specified in the DHCP 66 yiaddr-field 126. CMTS 12 uses the MAC44 address associated with the DHCP 66 chaddr-field 130 even if theBROADCAST bit is set.

CM 16 receives the DHCPACK message. It examines the DHCP 66 yiaddr-field126 and chaddr-field 132, and updates its routing table and an ARProuting table to reflect the address pairing at step 320. At step 322,CM 16 sends the DHCPACK message to CPE 18 via CMCI 20 at IP 54 and MAC44 addresses respectively from its routing tables. If the BROADCAST bitin the DHCP 66 flags-field 122 is set to one, CM 16 sends the downstreampacket to a broadcast IP 54 address (e.g., 255.255.255.255), instead ofthe address specified in DHCP 66 yiaddr-field 126. CM 16 uses the MAC 44address specified in DHCP 66 chaddr-field 132 even if the BROADCAST bitis set to located CPE 18. At step 324, CPE 18 receives the DHCPACK fromCM 16 and has established a virtual connection to data network 28.

In the event that CPE 18 is not compatible with the configurationreceived in the DHCPACK message, CPE 18 may generate a DHCP 66 decline("DHCPDECLINE") message and send it to CM 16. CM 16 will transmit theDHCPDECLINE message up the PPP 50 link via PSTN 22 to TRAC 24. On seeinga DHCPDECLINE message TRAC 24 sends a unicast copy of the message toCMTS 12. CM 16 and CMTS 12 examine the DHCP 66 yiaddr-field 126 andgiaddr-field 130, and update their routing and ARP tables to flush anyinvalid pairings.

Upon completion of methods 266 and 292, CM 16 CMTS 12 have valid IP/MACaddress pairings in their routing and ARP tables. These tables store thesame set of IP 54 addresses, but does not associate them with the sameMAC 44 addresses. This is because CMTS 12 resolves all CPE 18 IP 54addresses to the MAC 44 address of a corresponding CM 16. The CMs 16, onother hand, are able to address the respective MAC 44 addresses of theirCPEs 18. This also allows DHCP 66 clients associated with CPE 18 tofunction normally since the addressing that is done in CM 16 and CMTS 12is transparent to CPE 18 hosts.

FIG. 17 is a block diagram illustrating a message flow 326 for methods268 and 294 in FIGS. 15A, 15B, and 16A and 16B. Message flow 326illustrates a message flow for methods 268 and 294, for adata-over-cable system with and without telephony return. In anotherembodiment of the present invention, CM 16 forwards requests from CPE 18via an upstream connection on cable network 14 to DHCP servers 160associated with one or more network host interfaces available on CMTS12.

Method 268 and 294 accomplishes resolving addresses for networkinterface hosts from customer premise equipment in a data-over-cablewith or without telephony return without extensions to the existing DHCPprotocol. Methods 268 and 294 of the present invention are used indata-over-cable system 10 with telephony return. However, the presentinvention is not limited to data-over-cable system 10 with telephonyreturn and can be used in data-over-cable system 10 without telephonyreturn by using an upstream cable channel instead of an upstreamtelephony channel.

Secure cable modem initialization

FIG. 18 is a block diagram illustrating a data-over-cable system 330used for an illustrative embodiment of the present invention.Data-over-cable system 330 is similar to the data-over-cable systemillustrated in FIG. 8. However, FIG. 18 illustrates TFTP 64 server 332used to obtain configuration information 334 for CM 16. Exemplaryconfiguration information is illustrated in Type/Length/Value ("TLV")format in Table 10. However, more or fewer configuration parameterscould also be used. In addition, only a description of the Value in theTLV format is included since the actual numbers used for the Valuefields are implementation specific.

                  TABLE 10                                                        ______________________________________                                        Type       Length    Description of Value                                     ______________________________________                                        1          4         Receive frequency                                        2          1         Upstream channel identifier                              4x         N         Class of service header                                  41         1         Class identifier                                         42         4         Maximum downstream data                                                       rate in bits/sec                                         43         4         Maximum upstream data rate                                                    in bits/sec                                              44         1         Upstream channel priority                                45         4         Upstream guaranteed                                                           minimum data rate in bits/sec                            46         2         Maximum upstream                                                              configuration setting in                                                      minislots                                                47         1         Privacy enable                                           8          3         Vendor Identifier configuration                                               setting                                                  17x        N         Baseline privacy settings                                                     header                                                   171        4         Authorize timeout seconds                                172        4         Reauthorize wait timeout                                                      seconds                                                  173        4         Authorization wait timeout                                                    seconds                                                  174        4         Operational wait timeout                                                      seconds                                                  175        4         Re-key wait timeout seconds                              176        4         TEK grace time seconds                                   9          N         Software upgrade filename                                10         1         SNMP access control                                      11         N         Arbitrary SNMP object setting                            0          N         Padding for 4-byte boundary                              3          1         Network access                                           6          16        CM-MIC                                                   7          16        CMTS-MIC                                                 255        N/A       End-of-file                                              ______________________________________                                    

FIG. 19 is a flow diagram illustrating a method 336 for secureinitialization for a network device in a data-over-cable system. Method336 includes receiving a request for a first configuration file on afirst protocol server from a first network device at step 338. The firstconfiguration file includes multiple configuration parameters forinitializing the first network device (e.g., from Table 10). In oneembodiment, the requested configuration file is optionally obtained bythe first protocol server from another location at step 340. In anotherembodiment of the present invention, the requested configuration file isobtained from the first protocol server. A unique identifier (e.g., anetwork address) for the network device is added to the firstconfiguration file at step 342. In one embodiment of the presentinvention, the unique identifier is obtained by the first protocolserver from a header in the first message. A selected time-value (e.g.,a "time-now" value) is added to the first configuration file at step344. The selected time-value indicates an approximate sending time ofthe first configuration file. A message integrity check value iscalculated at step 346 using the unique identifier, selected time-valueand one or more configuration parameters from the configuration file ina pre-determined order to uniquely identify the configuration parametersfor the first network device. The message integrity check value iscalculated using a pre-determined cryptographic technique function. Themessage integrity check value is added to the first configuration fileat step 348. The first configuration file is sent from the firstprotocol server to the first network device at step 350.

The first network device uses the message integrity check value, theunique identifier and selected time-value to uniquely verify theintegrity of the configuration information and prevent another networkdevice from using the first configuration file at a later time. In anillustrative embodiment of the present invention, the first networkdevice is CM 16, the unique identifier is an IP 54 address for CM 16,and the first protocol server is TFTP server 332. However, the presentinvention is not limited to the illustrative embodiment and othernetwork devices, protocol servers, unique identifiers and messages indata-over-cable system 330 could also be used for secure initializationof a network device.

FIG. 20 is a flow diagram illustrating a method 352 for secureinitialization for a cable modem. Method 352 includes receiving a TFTP64 Read ReQuest message ("RRQ") for a first configuration file on TFTPserver 332 from CM 16 at step 354. The first configuration file includesmultiple configuration parameters (e.g., from Table 10) used toinitialize CM 16. TFTP server 332 obtains the requested firstconfiguration file at step 356. In one embodiment of the presentinvention, the first configuration file is obtained from DHCP server160. In another embodiment of the present invention, the firstconfiguration file is obtained from CMTS 12. In yet another embodimentof the present invention, the first configuration file is obtained fromTFTP server 332. A unique identifier (e.g., a network address) for CM 16is added to the first configuration file at step 358. In an illustrativeembodiment of the present invention, the unique identifier is an IP 54address that CM 16 received during the DHCP 66 initialization sequence(FIG. 12). However, other addresses or identifiers could also be used(e.g., MAC 44 address). In one embodiment of the present invention, theIP 54 address is obtained by TFTP server 332 from a header in the TFTP64 RRQ message sent from CM 16. In another embodiment of the presentinvention IP 54 address is obtained from a DHCP 66 message or anotherprotocol message. In another embodiment of the present invention, theunique identifier is a domain name for CM 16 (e.g.,cm1.data-over-cable.net). A TFTP 64 message header typically includes alocal medium header, an IP 54 header, a UDP header 60 and a TFTP 64header. For more information on the TFTP 64 header, see RFC-1350.However, other unique identifiers from other locations could also beused (e.g., a MAC 44 address for CM 16).

Table 11 illustrates a unique identifier in TLV format added to theconfiguration file. However, other unique identifier formats could alsobe used.

                  TABLE 11                                                        ______________________________________                                        Type       Length    Description of Value                                     ______________________________________                                        Y          4         Unique identifier, e.g., IP 54                                                address of CM 16                                         ______________________________________                                    

A selected time-value is added to the configuration file at step 360.The selected time-value is called a "time-now" value and indicates anapproximate sending time of the configuration file from TFTP server 332to CM 16. Table 12 illustrates a selected time value in TLV format.However, other selected time-value formats could also be used.

                  TABLE 12                                                        ______________________________________                                        Type       Length    Description of Value                                     ______________________________________                                        Z          4         Number of seconds since                                                       00:00 on January 1, 1970.                                                     (UNIX Epoch Time, RFC-868)                               ______________________________________                                    

The selected time value is used as defined in RFC-868; incorporatedherein by reference. However, the selected time-value is the number ofseconds since time 00:00, or midnight on Jan. 1, 1970 (i.e., UNIX epochtime) instead of since time 00:00, or midnight on Jan. 1, 1900. However,other time values and formats could also be used (e.g., seconds sinceboot time, or a common network clock time).

An additional field is used in the configuration file to indicate theaddition of configuration parameters such as the unique identifier andselected time-value to the configuration file. Table 13 illustrates aconfiguration file type TLV used for additional configurationparameters. However, other configuration file types could also be used.

                  TABLE 13                                                        ______________________________________                                        Type       Length    Description of Value                                     ______________________________________                                        T          1         Configuration File Version                               ______________________________________                                    

Table 14 illustrates values for the configuration file version values.However, more or fewer configuration file versions could also be used.

                  TABLE 14                                                        ______________________________________                                        Configuration File Version Value                                                               Definition of value                                          ______________________________________                                        0                Default, no additional configuration                                          parameters added.                                            1                Additional configuration parameters                                           added (e.g., unique identifier and                                            selected time-value)                                         ______________________________________                                    

Returning to FIG. 20, a Message Integrity Check ("MIC") value iscalculated using the unique identifier (Table 11), the selectedtime-value (Table 12) and one or more configuration parameters from theconfiguration information (Tables 10) in a pre-determined order touniquely identify the configuration file for CM 16 at step 362. Acryptographic hashing function is used to calculate the MIC Value.

In one embodiment of the present invention, authentication of theconfiguration information in the registration request message isprovided by two Message Integrity Check ("MIC") fields, "CM-MIC" and"CMTS-MIC" (Type 6 and Type 7, Table 10). The CM-MIC is a cryptographicdigest created with cryptographic hashing function (e.g., Message Digest5 ("MD5")) that ensures data sent from CM 16 is not modified en-route.CM-MIC is not an authenticated digest (i.e., it does not include anyshared secret password). The CMTS-MIC is also a cryptographic digestused authenticate configuration information.

In one embodiment of the present invention, MD5 cryptographic hashingfunction is used to create the CM-MIC and CMTS-MIC digests as describedin RFC-2104; incorporated herein by reference. However, othercryptographic hashing functions could also be used. As is known in thecryptography arts, MD5 is a secure, one-way hashing function used tocreate a secure hash value that is used to authenticate messages.

A CM-MIC value in a cable modem configuration file is calculated byperforming an MD5 digest over the bytes of the TLV entries for theconfiguration parameters. However, in an illustrative embodiment of thepresent invention, a CM-MIC value includes the unique identifier (Table11) and selected time-value (Table 12) that are added to theconfiguration file at steps 342 and 344 respectively of method 338, aswell as one or more of the configuration parameters illustrated in Table10.

A CMTS-MIC value is calculated for a cable modem configuration fileusing the method shown in Table 15.

                  TABLE 15                                                        ______________________________________                                        CMTS-MIC field for a cable modern configuration file is calculated by         performing an MD5 digest over the following configuration parameter           fields, when present in the configuration file, in the order shown:           • Downstream Frequency Configuration parameter                          • Upstream Channel ID Configuration parameter                           • Network Access Configuration parameter                                • Class of Service Configuration parameter                              • Vendor ID Configuration parameter                                     • Baseline Privacy Configuration parameters                             • Vendor specific Configuration parameters                              • CM-MIC Value                                                          • Authentication string.                                                The configuration parameter fields are treated as if they were                contiguous                                                                    data when calculating the MD 5 digest.                                        ______________________________________                                    

However, in an illustrative embodiment of the present invention, theCMTS-MIC value is calculated using the unique identifier (Table 11), theselected time-value (Table 12) and one or more configuration parameters(Table 15) in a pre-determined order. In another embodiment of thepresent invention a single MIC value is calculated using only the uniqueidentifier (Table 11) and the selected time-value (Table 12).

FIG. 21 is a flow diagram illustrating a method 368 to calculate amessage integrity value (e.g., at step 346 of method 336 or step 362 ofmethod 352). At step 370, a first message integrity value (e.g., CM-MIC)is calculated on one or more configuration parameters in apre-determined order. The one or more configuration parameters include aunique identifier (Table 11) and a selected-time value (Table 12) andone or more other configuration parameters (Table 15). At step 372, thefirst message integrity value is added to a configuration file. At step374, a second message integrity value (e.g., CMTS-MIC) is calculated onone or more configuration parameters and the first message integrityvalue in a pre-determined order. The second message integrity value iscalculated using the unique identifier (Table 11), the selected-timevalue (Table 12), the first message integrity value (e.g., CM-MIC), andone or more other additional configuration parameters (Table 15). Inanother embodiment of the present invention, the first and secondmessage integrity values are calculated using the unique identifier orthe selected time-value and one or more configuration parameters in apre-determined order. In yet another embodiment of the presentinvention, calculating the second message integrity includes the uniqueidentifier or the selected time-value and one or more additionalconfiguration parameters in a pre-determined order but does not includethe first message integrity value. In yet another embodiment of thepresent invention, the first message integrity value is not calculated,and only a second message integrity value is calculated using the uniqueidentifier and the selected time-value.

In an illustrative embodiment of the present invention, the firstmessage integrity value of method 368 is a CM-MIC, the second messageintegrity value is a CMTS-MIC and the configuration file is created byTFTP server 332 and sent to CM 16. However, other message integrityvalues and message integrity calculations could also be used.

Table 16 illustrates step 374 of method 368 for an illustrativeembodiment of the present invention for calculating the second messageintegrity value in a pre-determined order. However, more or fewerconfiguration parameters and other orderings could also be used.

                                      TABLE 16                                    __________________________________________________________________________      Use one or more of the configuration parameters from the configuration        file as shown in                                                              Table 15 when present in the order listed.                                    Use the unique identifier, selected time-value and one or more of the         configuration                                                                 parameters from Table 15 and calculate a MIC value by performing an MD5       digest                                                                        over the configuration parameters, when present in the configuration          file, in the order shown:                                                   •                                                                         One or more configuration parameters (Table 10, Table 15)                   •                                                                         Selected time-value (Table 12)                                              •                                                                         Network address (Table 11).                                                   Add the MIC value to the configuration file.                                __________________________________________________________________________

Returning again to FIG. 20, at step 364, the message integrity value(e.g., the CMTS-MIC value) is added to the configuration file. Themessage integrity value includes the unique identifier and selected timevalue added at steps 358 and 360 of method 352 and one or moreconfiguration parameters (Table 10). At step 366, the configuration filewith the message integrity value is sent from TFTP server 332 to CM 16via CMTS 12 and cable network 14 on a downstream cable televisionconnection.

Table 17 illustrates TLV data for an exemplary cable modem configurationfile to configure CM 16 to browse a data network 28 such as the Internetor an intranet. However, the present invention is not limited to theconfiguration file in Table 17 and more or fewer configurationparameters could also be used.

                  TABLE 17                                                        ______________________________________                                        Type  Length   Value          Notes                                           ______________________________________                                        T     1        1              Additional                                                                    configuration                                                                 parameters added                                4x    6        N/A            Header Length                                   41    1        1              Class-Of-Service-1                              42    4        1,500,000      Maximum                                                                       downstream data rate                                                          of 1.5 Mbps                                     43    4        256,000        Maximum upstream                                                              data rate of 256 Kbps                           44    1        5              Priority is level 5.                            45    4        8,000          Minimum upstream                                                              data rate of 8 Kbps                             47    1        1              Privacy enabled                                 171   4        1              Authorize timeouts                              3     1        1              Enable network                                                                access                                          Z     4        Selected time-value,                                                                         Time now for security                                          step 360                                                       Y     4        Network address, step                                                                        CM 16 IP 54 address                                            358            for security                                    0     N        N-byte padding Padding to make                                                               message 4-byte                                                                aligned                                         6     16       CM-MIC         MD5 digest for CM 16                            7     16       Message integrity                                                                            MD5 digest for CMTS                                            value, step 362                                                                              12 (e.g., CMTS-MIC)                             255   N/A                     End-of-file                                     ______________________________________                                    

In one embodiment of the present invention, CM 16 uses the messageintegrity check value including at least the unique identifier andselected time-value to uniquely identify the configuration file andprevent another rouge cable modem from using the configurationparameters in the configuration file at a later time.

FIG. 22 is a flow diagram illustrating a method 378 for checkingvalidity of a configuration file on a cable modem. At step 380, CM 16 aconfiguration file is received from TFTP server 332 created with method336 or method 352. At step 382, CM 16 determines if the configurationfile is authentic by checking a first message integrity in theconfiguration file. CM 16 calculates a second message integrity value onfields in the configuration file in a predetermined order (Table 16) andcompares it to the first message integrity check value. If the first andsecond message integrity values are the same, at step 384 CM 16determines if the configuration file was sent within a predeterminedtime limit by comparing a selected time-value (Table 12) in theconfiguration file to a current time-value in CM 16.

As was described above, the selected time-value is a time valueindicating an approximate time when the configuration file was sentbased on the number of seconds since time 00:00, or midnight on Jan. 1,1970. If the configuration file was not sent within a predetermined timelimit (e.g., 5 seconds), the configuration file is discarded at step386. In addition, if the configuration file was not authentic (step382), it is also discarded at step 386.

If the configuration file was authentic and was received with apredetermined time (e.g., 5 seconds), CM 16 accepts the configurationfile and uses the configuration parameters in the configuration file forconfiguration and initialization at step 388. CM 16 completesinitialization by sending CMTS 12 a registration request message withinformation from the configuration file as well additional configurationparameters. The registration request message allows CM 16 to registerwith CMTS 12 to receive data from data network 28 and cable network 14.

Since the registration request message is subject to similar attacks byrouge users as was described for the configuration file, CM 16 alsoincludes a unique identifier (i.e., CM 16 IP 54 address), a newselected-time value for sending the registration message and new amessage integrity value in a secure registration request message usingmethods similar to the methods 336, 352 and 368 described above for anillustrative embodiment of the present invention. Sending a secureregistration request message from CM 16 to CMTS 12 is described inco-pending Application No. assigned to the same assignee as the presentapplication.

In an illustrative embodiment of the present invention, TFTP server 332is called a "secure TFTP server" since configuration information for CM16 is sent using an IP 54 address for CM 16 extracted from the TFTP RRQmessage, a selected time-value indicating an approximate sending time ofa configuration file to CM 16, and a message integrity check valuecalculated using IP 54 address, selected time-value and one or moreother configuration parameters in a pre-determined order. Using methods336, 352 and/or 368 in a secure TFTP server allows a cable modem toobtain configuration information from a TFTP server in a more securemanner.

An illustrative embodiment of the present invention provides improvedsecure cable modem initialization. For a rouge user to attack adata-over-cable system, the rouge user must intercept a configurationfile, modify the selected time-value (on IP 54 address), re-calculatemessage integrity value with a rouge selected time value, andre-transmit the configuration file all within a pre-determined timeperiod that is used by the cable modem (e.g., 5 seconds) for checkingconfiguration files. Thus, an illustrative embodiment of the presentinvention reduces the possibility of attack by a rouge user and improvessecurity in a data-over-cable system.

It should be understood that the programs, processes, methods, systemsand apparatus described herein are not related or limited to anyparticular type of computer apparatus (hardware or software), unlessindicated otherwise. Various types of general purpose or specializedcomputer apparatus may be used with or perform operations in accordancewith the teachings described herein.

In view of the wide variety of embodiments to which the principles ofthe invention can be applied, it should be understood that theillustrated embodiments are exemplary only, and should not be taken aslimiting the scope of the present invention. For example, the steps ofthe flow diagrams may be taken in sequences other than those described,and more or fewer elements or component may be used in the blockdiagrams.

The claims should not be read as limited to the described order orelements unless stated to that effect. In addition, use of the term"means" in any claim is intended to invoke 35 U.S.C. § 112, paragraph 6,and any claim without the word "means" is not so intended. Therefore,all embodiments that come within the scope and spirit of the followingclaims and equivalents thereto are claimed as the invention.

I claim:
 1. In a data-over-cable system including a plurality of networkdevices, a method of securely initializing a network device, the methodcomprising the following steps:receiving a request a for firstconfiguration file on a first protocol server from a first networkdevice, the first configuration file including a plurality ofconfiguration parameters to initialize the first network device; addinga unique identifier for the first network device to the firstconfiguration file; adding a selected time-value to the firstconfiguration file, wherein the selected time-value indicates a sendingtime for the first configuration file; calculating a message integritycheck value using the unique identifier, the selected time-value and oneor more configuration parameters from the first configuration file in apre-determined order to uniquely identify the first configuration filefor the network device; adding the message integrity check value to thefirst configuration file; and sending the first configuration file fromthe first protocol server to the first network device, wherein the firstnetwork device uses the message integrity check value, the uniqueidentifier and the selected-time value indicating when the first messagewas sent from the first protocol server to verify the integrity of firstconfiguration file.
 2. A computer readable medium having stored thereininstructions for causing a central processing unit to execute the methodof claim
 1. 3. The method of claim 1 wherein the step of calculating amessage integrity check value includes calculating the message integritycheck value with a cryptographic hashing function.
 4. The method ofclaim 3 wherein the cryptographic hashing function is MD5.
 5. The methodof claim 1 wherein the step of adding a unique identifier for the firstnetwork device to the configuration file includes adding an InternetProtocol address for the first network device to the first configurationfile.
 6. The method of claim 1 wherein the first network device is acable modem and the first protocol server is a secure Trivial FileTransfer Protocol server.
 7. The method of claim 1 wherein the firstconfiguration file is a cable modem configuration file used toinitialize a cable modem in the data-over-cable system.
 8. The messageof claim 1 wherein the selected time-value is a number of seconds thefirst network device has been executing.
 9. The method of claim 8wherein the number of seconds the first network device has beenexecuting includes the number of seconds the first network device hasbeen executing since time 00:00 on Jan. 1,
 1970. 10. The method of claim1 wherein the step of calculating a message integrity check valueincludes:calculating a first message integrity value using the uniqueidentifier, the selected time-value and one or more configurationparameters from the first configuration file in a predetermined order;adding the first message integrity value to the first configurationfile; calculating a second message integrity value using the uniqueidentifier, the selected time-value, one or more configurationparameters from the first configuration file and the first messageintegrity value in a pre-determined order; and adding the second messageintegrity value to first configuration file as the message integrityvalue.
 11. In a data-over-cable system including a plurality of networkdevices, a method of securely initializing a network device, the methodcomprising the following steps:receiving a first configuration file on afirst network device from a first protocol server; and determiningwhether the first configuration file is valid using a message integritycheck value included in the first configuration file, and ifso,determining whether the first configuration file was sent within apre-determined time using a selected time-value from the firstconfiguration file, and if not,rejecting the first configuration file onthe first network device.
 12. A computer readable medium having storedtherein instructions for causing a central processing unit to executethe method of claim
 11. 13. The method of claim 11 wherein the firstnetwork device is a cable modem and the first protocol server is asecure Trivial File Transfer Protocol server.
 14. The method of claim 11wherein the message integrity check value includes a first uniqueidentifier for the first network device, a selected time-valueindicating a sending time for the first configuration file and aplurality of configuration parameters used to configure the firstnetwork device.
 15. The method of claim 11 wherein the step ofdetermining whether the first configuration file is valid using amessage integrity check value included in the first configuration fileincludes calculating a second message integrity value using acryptographic hashing function and comparing it to the message integritycheck value.
 16. The method of claim 15 wherein the cryptographichashing function is MD5.
 17. The method of claim 11 furthercomprising:determining whether the first configuration file was sentwithin a predetermined time using a selected time-value from the firstmessage integrity check value, wherein the first message integrity checkvalue includes a unique identifier for the first network device and aselected time-value, and if so, accepting the configuration file onfirst network device; and initializing the first network device usingconfiguration parameters from the first configuration file.
 18. A secureprotocol server for transferring a configuration file to a networkdevice, the secure protocol server comprising:unique identifierextractor, for extracting a unique identifier for a network device froma request message to uniquely identify the configuration file for thenetwork device; time-value selector, for selecting a time-value that isadded to the configuration file and used to indicate a send time for theconfiguration file; message integrity value calculator, for calculatinga message integrity value using the unique identifier, selectedtime-value and one or more configuration parameters to uniquely identifythe configuration file for a network device.
 19. The secure protocolserver of claim 18 wherein the secure protocol server is a secureTrivial File Transfer Protocol server.
 20. The secure protocol server ofclaim 18 wherein the network device is a cable modem and the uniqueidentifier selector selects an Internet Protocol address for a networkdevice.
 21. In a data-over-cable system including a plurality of cablemodems, a method of securely initializing a cable modem, the methodcomprising the following steps:receiving a request for a firstconfiguration file on a Trivial File Transfer Protocol server from acable modem, the first configuration file including a plurality ofconfiguration parameters to initialize the cable modem; adding anInternet Protocol address for the cable modem to the first configurationfile; adding a selected time-value to the first configuration file,wherein the selected time-value indicates a sending time for therequested first configuration file; calculating a message integritycheck value using a cryptographic hashing function with the InternetProtocol address, the selected time-value and one or more configurationparameters from the first configuration file in a predetermined order touniquely identify the first configuration file for the cable modem;adding the message integrity check value to the first configurationfile; and sending the first configuration file from the Trivial FileTransfer Protocol server to the cable modem, wherein the cable modemuses the message integrity check value, the unique identifier and theselected time-value indicating when the first configuration file wassent to the cable modem from the Trivial File Transfer Protocol serverto verify the integrity of the first configuration file.
 22. A computerreadable medium having stored therein instructions for causing a centralprocessing unit to execute the method of claim 21.